chore(package): update webpack to version 4.8.2

Closes #47

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
     "grunt-mocha-test": "^0.13.2",
     "mocha": "^4.0.0",
     "phantomjs-prebuilt": "^2.1.12",
-    "webpack": "^3.5.0"
+    "webpack": "^4.8.2"
   },
   "dependencies": {
     "coffee-script": "^1.12.0",