chore(package): update karma-webpack to version 4.0.1

Closes #28

Author: greenkeeper[bot]

package.json

@@ -84,7 +84,7 @@
         "karma-sinon": "^1.0.5",
         "karma-sourcemap-loader": "^0.3.7",
         "karma-sourcemap-writer": "^0.1.2",
-        "karma-webpack": "^3.0.5",
+        "karma-webpack": "^4.0.1",
         "mocha": "^5.2.0",
         "phaser": "^3.16.2",
         "prettier": "^1.16.4",