chore(deps): update dependency webpack-hot-middleware to v2.20.0

Author: renovate[bot]

package-lock.json

@@ -99,6 +99,6 @@
     "vue-template-compiler": "2.5.2",
     "webpack": "3.7.1",
     "webpack-dev-middleware": "1.12.0",
-    "webpack-hot-middleware": "2.19.1"
+    "webpack-hot-middleware": "2.20.0"
   }
 }