Merge branch 'dev' of https://github.com/dcloudio/uni-app into alpha

packages/vue-cli-plugin-uni/lib/mp.js

@@ -205,7 +205,9 @@ module.exports = {
           cssnanoOptions: {
             preset: [
               'default',
-              getPlatformCssnano()
+              Object.assign({}, getPlatformCssnano(), {
+                discardComments: true
+              })
             ]
           }