Remove json-loader from base webpack config

With the webpack 4+, you don't need to specify the json-loader in your webpack config. 
Instead, you can simply import the .json files like this
```
import customConfig from "./config.json";
```

Author: verdan

config/webpack.base.babel.js

@@ -70,10 +70,6 @@ module.exports = (options) => ({
         test: /\.html$/,
         use: 'html-loader'
       },
-      {
-        test: /\.json$/,
-        use: 'json-loader'
-      },
       {
         test: /\.(mp4|webm)$/,
         use: {