feat(package.json): Bump webpack to 4.2.0

Author: halfzebra

package.json

@@ -53,7 +53,7 @@
     "sw-precache-webpack-plugin": "^0.11.5",
     "uglifyjs-webpack-plugin": "^1.2.4",
     "url-loader": "^1.0.1",
-    "webpack": "^4.1.1",
+    "webpack": "^4.2.0",
     "webpack-dev-server": "^3.1.1",
     "webpack-manifest-plugin": "^2.0.0-rc.2"
   },