Bumps uglifyjs-webpack-plugin and its dependencies.

Solves a GitHub warning about a vulnerability in a
uglifyjs-webpack-plugin dependency.

package-lock.json

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     },
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         "graceful-fs": "4.1.11",
         "lru-cache": "4.1.1",
-        "mississippi": "1.3.0",
+        "mississippi": "2.0.0",
         "mkdirp": "0.5.1",
         "move-concurrently": "1.0.1",
         "promise-inflight": "1.0.1",
         "rimraf": "2.6.2",
-        "ssri": "5.1.0",
+        "ssri": "5.2.4",
         "unique-filename": "1.1.0",
-        "y18n": "3.2.1"
+        "y18n": "4.0.0"
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       "dev": true,
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       "dev": true
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-      "resolved": "https://registry.npmjs.org/mississippi/-/mississippi-1.3.0.tgz",
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       "dev": true,
       "requires": {
         "concat-stream": "1.6.0",
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+        "duplexify": "3.5.4",
         "end-of-stream": "1.4.1",
         "flush-write-stream": "1.0.2",
         "from2": "2.3.0",
         "parallel-transform": "1.1.0",
-        "pump": "1.0.3",
+        "pump": "2.0.1",
         "pumpify": "1.4.0",
         "stream-each": "1.2.2",
         "through2": "2.0.3"
       }
     },
     "pump": {
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-      "resolved": "https://registry.npmjs.org/pump/-/pump-1.0.3.tgz",
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+      "resolved": "https://registry.npmjs.org/pump/-/pump-2.0.1.tgz",
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       "dev": true,
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       "dev": true,
       "requires": {
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+        "duplexify": "3.5.4",
         "inherits": "2.0.3",
-        "pump": "2.0.0"
-      },
-      "dependencies": {
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-          "dev": true,
-          "requires": {
-            "end-of-stream": "1.4.1",
-            "once": "1.4.0"
-          }
-        }
+        "pump": "2.0.1"
       }
     },
     "punycode": {
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     },
     "schema-utils": {
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-      "resolved": "https://registry.npmjs.org/schema-utils/-/schema-utils-0.3.0.tgz",
-      "integrity": "sha1-9YdyIs4+kx7a4DnxfrNxbnE3+M8=",
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+      "resolved": "https://registry.npmjs.org/schema-utils/-/schema-utils-0.4.5.tgz",
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       "dev": true,
       "requires": {
-        "ajv": "5.5.2"
+        "ajv": "6.2.1",
+        "ajv-keywords": "3.1.0"
+      },
+      "dependencies": {
+        "ajv": {
+          "version": "6.2.1",
+          "resolved": "https://registry.npmjs.org/ajv/-/ajv-6.2.1.tgz",
+          "integrity": "sha1-KKarxJOiq+D7TIUHrK7bQ/pVBnE=",
+          "dev": true,
+          "requires": {
+            "fast-deep-equal": "1.0.0",
+            "fast-json-stable-stringify": "2.0.0",
+            "json-schema-traverse": "0.3.1"
+          }
+        },
+        "ajv-keywords": {
+          "version": "3.1.0",
+          "resolved": "https://registry.npmjs.org/ajv-keywords/-/ajv-keywords-3.1.0.tgz",
+          "integrity": "sha1-rCsnk5xUPpXSwG5/f1wnvkqlQ74=",
+          "dev": true
+        }
       }
     },
     "sdp": {
       "integrity": "sha512-4SJ3dm0WAwWy/NVeioZh5AntkdJoWKxHxcmyP622fOkgHa4z3R0TdBJICINyaSDE6uNwVc8gZr+ZinwZAH4xIA==",
       "dev": true
     },
+    "serialize-javascript": {
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/serialize-javascript/-/serialize-javascript-1.4.0.tgz",
+      "integrity": "sha1-fJWFFNtqwkQ6irwGLcn3iGp/YAU=",
+      "dev": true
+    },
     "set-blocking": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/set-blocking/-/set-blocking-2.0.0.tgz",
       }
     },
     "ssri": {
-      "version": "5.1.0",
-      "resolved": "https://registry.npmjs.org/ssri/-/ssri-5.1.0.tgz",
-      "integrity": "sha512-TevC8fgxQKTfQ1nWtM9GNzr3q5rrHNntG9CDMH1k3QhSZI6Kb+NbjLRs8oPFZa2Hgo7zoekL+UTvoEk7tsbjQg==",
+      "version": "5.2.4",
+      "resolved": "https://registry.npmjs.org/ssri/-/ssri-5.2.4.tgz",
+      "integrity": "sha512-UnEAgMZa15973iH7cUi0AHjJn1ACDIkaMyZILoqwN6yzt+4P81I8tBc5Hl+qwi5auMplZtPQsHrPBR5vJLcQtQ==",
       "dev": true,
       "requires": {
         "safe-buffer": "5.1.1"
       "dev": true
     },
     "uglify-es": {
-      "version": "3.3.7",
-      "resolved": "https://registry.npmjs.org/uglify-es/-/uglify-es-3.3.7.tgz",
-      "integrity": "sha512-fGMnE6SsDRsCjxm78C+lv7MuXsse/dtF7QuTUT43BYf4jlxPjd+XTnGB8YjaCQJ3sv2LT4zk0mwpp9+QJocU6g==",
+      "version": "3.3.9",
+      "resolved": "https://registry.npmjs.org/uglify-es/-/uglify-es-3.3.9.tgz",
+      "integrity": "sha512-r+MU0rfv4L/0eeW3xZrd16t4NZfK8Ld4SWVglYBb7ez5uXFWHuVRs6xCTrf1yirs9a4j4Y27nn7SRfO6v67XsQ==",
       "dev": true,
       "requires": {
         "commander": "2.13.0",
       "optional": true
     },
     "uglifyjs-webpack-plugin": {
-      "version": "1.1.2",
-      "resolved": "https://registry.npmjs.org/uglifyjs-webpack-plugin/-/uglifyjs-webpack-plugin-1.1.2.tgz",
-      "integrity": "sha512-k07cmJTj+8vZMSc3BaQ9uW7qVl2MqDts4ti4KaNACXEcXSw2vQM2S8olSk/CODxvcSFGvUHzNSqA8JQlhgUJPw==",
+      "version": "1.2.2",
+      "resolved": "https://registry.npmjs.org/uglifyjs-webpack-plugin/-/uglifyjs-webpack-plugin-1.2.2.tgz",
+      "integrity": "sha512-CG/NvzXfemUAm5Y4Guh5eEaJYHtkG7kKNpXEJHp9QpxsFVB5/qKvYWoMaq4sa99ccZ0hM3MK8vQV9XPZB4357A==",
       "dev": true,
       "requires": {
-        "cacache": "10.0.2",
+        "cacache": "10.0.4",
         "find-cache-dir": "1.0.0",
-        "schema-utils": "0.3.0",
+        "schema-utils": "0.4.5",
+        "serialize-javascript": "1.4.0",
         "source-map": "0.6.1",
-        "uglify-es": "3.3.7",
+        "uglify-es": "3.3.9",
         "webpack-sources": "1.1.0",
-        "worker-farm": "1.5.2"
+        "worker-farm": "1.5.4"
       },
       "dependencies": {
         "source-map": {
       "dev": true
     },
     "worker-farm": {
-      "version": "1.5.2",
-      "resolved": "https://registry.npmjs.org/worker-farm/-/worker-farm-1.5.2.tgz",
-      "integrity": "sha512-XxiQ9kZN5n6mmnW+mFJ+wXjNNI/Nx4DIdaAKLX1Bn6LYBWlN/zaBhu34DQYPZ1AJobQuu67S2OfDdNSVULvXkQ==",
+      "version": "1.5.4",
+      "resolved": "https://registry.npmjs.org/worker-farm/-/worker-farm-1.5.4.tgz",
+      "integrity": "sha512-ITyClEvcfv0ozqJl1vmWFWhvI+OIrkbInYqkEPE50wFPXj8J9Gd3FYf8+CkZJXJJsQBYe+2DvmoK9Zhx5w8W+w==",
       "dev": true,
       "requires": {
-        "errno": "0.1.6",
+        "errno": "0.1.7",
         "xtend": "4.0.1"
+      },
+      "dependencies": {
+        "errno": {
+          "version": "0.1.7",
+          "resolved": "https://registry.npmjs.org/errno/-/errno-0.1.7.tgz",
+          "integrity": "sha512-MfrRBDWzIWifgq6tJj60gkAwtLNb6sQPlcFrSOflcP1aFmmruKQ2wRnze/8V6kgyz7H3FF8Npzv78mZ7XLLflg==",
+          "dev": true,
+          "requires": {
+            "prr": "1.0.1"
+          }
+        }
       }
     },
     "wrap-ansi": {

package.json

     "karma-webpack": "1.8.1",
     "precommit-hook": "3.0.0",
     "string-replace-loader": "1.3.0",
-    "uglifyjs-webpack-plugin": "1.1.2",
+    "uglifyjs-webpack-plugin": "1.2.2",
     "webpack": "3.9.1"
   },
   "scripts": {