chore(package): update webpack to version 4.40.2

Closes #19

Author: greenkeeper[bot]

package.json

@@ -54,7 +54,7 @@
     "ts-loader": "^3.1.1",
     "tslint": "^5.8.0",
     "typescript": "^2.6.1",
-    "webpack": "^3.8.1"
+    "webpack": "^4.40.2"
   },
   "peerDependencies": {
     "react": "^15.0.0-0 || ^16.0.0-0"