chore(webpack): update webpack version to .21 (#1764)

* chore(webpack): update webpack version to 2.1.0-beta.21

Author: TheLarkInn

package.json

@@ -93,7 +93,7 @@
     "typedoc": "^0.4.2",
     "typescript": "^2.0.0",
     "url-loader": "^0.5.7",
-    "webpack": "2.1.0-beta.18",
+    "webpack": "2.1.0-beta.21",
     "webpack-dev-server": "2.1.0-beta.0",
     "webpack-md5-hash": "0.0.5",
     "webpack-merge": "^0.14.0"