自定义环境， test

1. 增加脚本
   "test:mp-weixin": "cross-env NODE_ENV=test UNI_PLATFORM=mp-weixin vue-cli-service uni-build --watch"
2. 点击
   'yarn test:mp-weixin'
3. 查看

ERROR  WebpackOptionsValidationError: Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.  
 - configuration.mode should be one of these:  
   "development" | "production" | "none"  
   -> Enable production optimizations or development hints.  
WebpackOptionsValidationError: Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.  
 - configuration.mode should be one of these:  
   "development" | "production" | "none"  
   -> Enable production optimizations or development hints.  
    at webpack (/Users/jimmy/MiniProjects/uni-cli-ts/node_modules/webpack/lib/webpack.js:31:9)  
    at serve (/Users/jimmy/MiniProjects/uni-cli-ts/node_modules/@dcloudio/vue-cli-plugin-uni/commands/serve.js:135:22)  
    at processTicksAndRejections (internal/process/task_queues.js:93:5)  
error Command failed with exit code 1.  
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.