fix: fix options for css optimize plugin (close #918)

Author: yyx990803

Diff for: packages/@vue/cli-service/lib/config/prod.js

@@ -20,11 +20,11 @@ module.exports = (api, options) => {
       // optimize CSS (dedupe)
       webpackConfig
         .plugin('optimize-css')
-          .use(require('optimize-css-assets-webpack-plugin'), [
-            options.productionSourceMap && options.cssSourceMap
+          .use(require('optimize-css-assets-webpack-plugin'), [{
+            cssProcessorOptions: options.productionSourceMap && options.cssSourceMap
               ? { safe: true, map: { inline: false }}
               : { safe: true }
-          ])
+          }])
 
       // minify JS
       const UglifyPlugin = require('uglifyjs-webpack-plugin')