chore(package): update karma-webpack to version 4.0.0

Closes #50

Author: greenkeeper[bot]

package.json

@@ -74,7 +74,7 @@
     "karma-phantomjs-launcher": "1.0.2",
     "karma-sauce-launcher": "1.1.0",
     "karma-sourcemap-loader": "0.3.7",
-    "karma-webpack": "1.8.0",
+    "karma-webpack": "4.0.0",
     "mkdirp": "0.5.1",
     "mocha": "3.2.0",
     "nyc": "10.0.0",