Make skygear easier to include in a webpack project

localforage to 1.4.2, it support es6 and webpack since 1.3.3
Use browser WebSocket if websocket is not install, it allow webpack to
configure to use browser WebSocket if set 'websocket' as external.

lib/pubsub.js

@@ -14,7 +14,13 @@
  * limitations under the License.
  */
 const _ = require('lodash');
-const WebSocket = require('websocket').w3cwebsocket;
+const _ws = require('websocket');
+let WebSocket = null;
+if (_ws) {
+  WebSocket = _ws.w3cwebsocket;
+} else {
+  WebSocket = window.WebSocket; //eslint-disable-line
+}
 const url = require('url');
 const ee = require('event-emitter');
 

package.json

@@ -61,15 +61,15 @@
     "babel-polyfill": "^6.1.19",
     "cookie-storage": "^1.0.4",
     "event-emitter": "^0.3.4",
-    "localforage": "~1.2.10",
     "localstorage-memory": "^1.0.2",
+    "localforage": "^1.4.2",
     "lodash": "^3.10.1",
     "md5": "^2.0.0",
     "superagent": "^1.3.0",
     "url": "^0.11.0",
     "uuid": "^2.0.1",
     "w3c-blob": "0.0.1",
-    "websocket": "^1.0.22"
+    "websocket": "^1.0.23"
   },
   "bugs": {
     "url": "https://github.com/SkygearIO/skygear-SDK-JS/issues"