chore(package): update webpack to version 4.15.1 (#292)

package.json

@@ -93,7 +93,7 @@
     "typescript": "^2.6.1",
     "uglifyjs-webpack-plugin": "^1.2.4",
     "underscore-template-loader": "^1.0.0",
-    "webpack": "^4.2.0",
+    "webpack": "^4.15.1",
     "webpack-cli": "^3.0.8",
     "webpack-dev-server": "3.1.3",
     "webpack-merge": "^4.1.2",