update karma-webpack to v4

Author: gfx

package-lock.json

@@ -73,7 +73,7 @@
     "karma-mocha": "^1.3.0",
     "karma-sauce-launcher": "^2.0.2",
     "karma-sourcemap-loader": "^0.3.7",
-    "karma-webpack": "^3.0.5",
+    "karma-webpack": "^4.0.2",
     "lodash": "^4.17.11",
     "mocha": "^6.1.4",
     "msgpack-test-js": "^1.0.0",