Fixed html-webpack-plugin version

package.json

@@ -43,7 +43,7 @@
     "eventsource-polyfill": "0.9.6",
     "file-loader": "1.1.11",
     "friendly-errors-webpack-plugin": "1.7.0",
-    "html-webpack-plugin": "^4.0.0-alpha",
+    "html-webpack-plugin": "4.0.0-alpha",
     "mini-css-extract-plugin": "0.4.1",
     "node-notifier": "5.2.1",
     "node-sass": "^4.7.2",