deps: update clean-css (reland)

Fix the incorrect paths (was a breaking change in version 4) by using the
`--skip-rebase` cli option.

Makefile

 
 deploy-css:
 	$(NODE_SASS) $(STYLES_MAIN) $(STYLES_BUNDLE) && \
-	$(CLEANCSS) $(STYLES_BUNDLE) > $(STYLES_DESTINATION) ; \
+	$(CLEANCSS) --skip-rebase $(STYLES_BUNDLE) > $(STYLES_DESTINATION) ; \
 	rm $(STYLES_BUNDLE)
 
 deploy-local:

package-lock.json

       "resolved": "https://registry.npmjs.org/classnames/-/classnames-2.2.5.tgz",
       "integrity": "sha1-+zgB1FNGdknvNgPH1hoCvRKb3m0="
     },
-    "clean-css": {
-      "version": "3.4.25",
-      "resolved": "https://registry.npmjs.org/clean-css/-/clean-css-3.4.25.tgz",
-      "integrity": "sha1-nppS1cHmvFEj4bJ4P6Zf6ViUbt4=",
+    "clean-css-cli": {
+      "version": "4.3.0",
+      "resolved": "https://registry.npmjs.org/clean-css-cli/-/clean-css-cli-4.3.0.tgz",
+      "integrity": "sha512-8GHZfr+mG3zB/Lgqrr27qHBFsPSn0fyEI3f2rIZpxPxUbn2J6A8xyyeBRVTW8duDuXigN0s80vsXiXJOEFIO5Q==",
       "dev": true,
       "requires": {
-        "commander": "2.8.x",
-        "source-map": "0.4.x"
+        "clean-css": "^4.2.1",
+        "commander": "2.x",
+        "glob": "7.x"
       },
       "dependencies": {
-        "commander": {
-          "version": "2.8.1",
-          "resolved": "https://registry.npmjs.org/commander/-/commander-2.8.1.tgz",
-          "integrity": "sha1-Br42f+v9oMMwqh4qBy09yXYkJdQ=",
+        "clean-css": {
+          "version": "4.2.3",
+          "resolved": "https://registry.npmjs.org/clean-css/-/clean-css-4.2.3.tgz",
+          "integrity": "sha512-VcMWDN54ZN/DS+g58HYL5/n4Zrqe8vHJpGA8KdgUXFU4fuP/aHNw8eld9SyEIyabIMJX/0RaY/fplOo5hYLSFA==",
           "dev": true,
           "requires": {
-            "graceful-readlink": ">= 1.0.0"
+            "source-map": "~0.6.0"
           }
         },
         "source-map": {
-          "version": "0.4.4",
-          "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.4.4.tgz",
-          "integrity": "sha1-66T12pwNyZneaAMti092FzZSA2s=",
-          "dev": true,
-          "requires": {
-            "amdefine": ">=0.0.4"
-          }
+          "version": "0.6.1",
+          "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
+          "integrity": "sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==",
+          "dev": true
         }
       }
     },
       "resolved": "https://registry.npmjs.org/graceful-fs/-/graceful-fs-4.1.11.tgz",
       "integrity": "sha1-Dovf5NHduIVNZOBOp8AOKgJuVlg="
     },
-    "graceful-readlink": {
-      "version": "1.0.1",
-      "resolved": "https://registry.npmjs.org/graceful-readlink/-/graceful-readlink-1.0.1.tgz",
-      "integrity": "sha1-TK+tdrxi8C+gObL5Tpo906ORpyU=",
-      "dev": true
-    },
     "growly": {
       "version": "1.3.0",
       "resolved": "https://registry.npmjs.org/growly/-/growly-1.3.0.tgz",

package.json

     "babel-eslint": "10.0.1",
     "babel-loader": "8.0.4",
     "circular-dependency-plugin": "5.2.0",
-    "clean-css": "3.4.25",
+    "clean-css-cli": "4.3.0",
     "css-loader": "3.6.0",
     "eslint": "5.6.1",
     "eslint-config-jitsi": "github:jitsi/eslint-config-jitsi#1.0.3",