deps: update react-native-webrtc dependency

It includes a W3C-ish permissions API which we will leverage.

package-lock.json

       }
     },
     "react-native-webrtc": {
-      "version": "github:jitsi/react-native-webrtc#111da886907024801bb3c90116708c6aad6dbba4",
-      "from": "github:jitsi/react-native-webrtc#111da886907024801bb3c90116708c6aad6dbba4",
+      "version": "github:jitsi/react-native-webrtc#be3de15bb988cfabbb62cd4b3b06f4c920ee5ba0",
+      "from": "github:jitsi/react-native-webrtc#be3de15bb988cfabbb62cd4b3b06f4c920ee5ba0",
       "requires": {
         "base64-js": "^1.1.2",
         "event-target-shim": "^1.0.5",

package.json

     "react-native-prompt": "1.0.0",
     "react-native-sound": "0.10.9",
     "react-native-vector-icons": "4.4.2",
-    "react-native-webrtc": "github:jitsi/react-native-webrtc#111da886907024801bb3c90116708c6aad6dbba4",
+    "react-native-webrtc": "github:jitsi/react-native-webrtc#be3de15bb988cfabbb62cd4b3b06f4c920ee5ba0",
     "react-redux": "5.0.7",
     "redux": "4.0.0",
     "redux-thunk": "2.2.0",