Merge pull request #2568 from Jonny-china/dev

feat: 自定义条件编译，支持 --mode

packages/vue-cli-plugin-uni/index.js

@@ -83,7 +83,9 @@ module.exports = (api, options) => {
   })
 }
 
+const args = require('minimist')(process.argv.slice(2))
+
 module.exports.defaultModes = {
-  'uni-serve': 'development',
-  'uni-build': process.env.NODE_ENV
-}
+  'uni-serve': args.mode || 'development',
+  'uni-build':  args.mode || process.env.NODE_ENV
+}