Remove webpack-merge dependency (#9)

package.json

@@ -49,8 +49,7 @@
     "typescript-formatter": "7.1.0",
     "webpack": "^4.43.0",
     "webpack-cli": "^3.3.11",
-    "webpack-dev-server": "^3.8.0",
-    "webpack-merge": "^4.1.4"
+    "webpack-dev-server": "^3.8.0"
   },
   "jest-junit": {
     "outputDirectory": "nyc",