fixed html-webpack-plugin version

package.json

@@ -85,7 +85,7 @@
     "file-loader": "1.1.11",
     "friendly-errors-webpack-plugin": "1.7.0",
     "hash-sum": "1.0.2",
-    "html-webpack-plugin": "^4.0.0-alpha",
+    "html-webpack-plugin": "4.0.0-alpha",
     "husky": "0.14.3",
     "lint-staged": "7.2.2",
     "mini-css-extract-plugin": "0.4.1",