chore(package): update webpack to version 4.28.4

Closes #11

Author: greenkeeper[bot]

package.json

@@ -41,7 +41,7 @@
     "tslint": "5.11.0",
     "typescript": "^3.0.1",
     "uglifyjs-webpack-plugin": "^2.0.0",
-    "webpack": "4.17.0",
+    "webpack": "4.28.4",
     "webpack-cli": "3.1.0",
     "webpack-dev-server": "3.1.6"
   },