fix(plugin-vue): allow to overwrite feature flags (#2675)

Author: fahchen

Diff for: packages/plugin-vue/src/index.ts

@@ -76,11 +76,12 @@ export default function vuePlugin(rawOptions: Options = {}): Plugin {
       return handleHotUpdate(ctx)
     },
 
-    config() {
+    config(config) {
       return {
         define: {
           __VUE_OPTIONS_API__: true,
-          __VUE_PROD_DEVTOOLS__: false
+          __VUE_PROD_DEVTOOLS__: false,
+          ...config.define
         },
         ssr: {
           external: ['vue', '@vue/server-renderer']