fix: use vue-cli default source-map (#3097)

cheap-module-eval-source-map

Author: PanJiaChen

vue.config.js

@@ -80,12 +80,6 @@ module.exports = {
       })
       .end()
 
-    config
-      // https://webpack.js.org/configuration/devtool/#development
-      .when(process.env.NODE_ENV === 'development',
-        config => config.devtool('cheap-source-map')
-      )
-
     config
       .when(process.env.NODE_ENV !== 'development',
         config => {