feat: vue.config devBaseUrl (fix #1102)

packages/@vue/cli-service/lib/config/dev.js

@@ -1,10 +1,10 @@
-module.exports = api => {
+module.exports = (api, options) => {
   api.chainWebpack(webpackConfig => {
     if (process.env.NODE_ENV === 'development') {
       webpackConfig
         .devtool('cheap-module-eval-source-map')
         .output
-          .publicPath('/')
+          .publicPath(options.devBaseUrl || '/')
 
       webpackConfig
         .plugin('hmr')

packages/@vue/cli-service/lib/options.js

@@ -2,6 +2,7 @@ const { createSchema, validate } = require('@vue/cli-shared-utils')
 
 const schema = createSchema(joi => joi.object({
   baseUrl: joi.string(),
+  devBaseUrl: joi.string(),
   outputDir: joi.string(),
   compiler: joi.boolean(),
   productionSourceMap: joi.boolean(),