docs(zh): the plugin-dev in zh has a regexp missing the end / (#6623)

Co-authored-by: 大宝 <[email protected]>

Author: HelloJiya

docs/zh/dev-guide/plugin-dev.md

@@ -152,7 +152,7 @@ export default {
 extend: '@vue/cli-service/generator/template/src/App.vue'
 replace:
   - !!js/regexp /Welcome to Your Vue\.js App/
-  - !!js/regexp /<script>[^]*?<\/script>
+  - !!js/regexp /<script>[^]*?<\/script>/
 ---
 
 <%# REPLACE %>