update

Author: kazupon

README.md

@@ -22,23 +22,13 @@ If yon don't have a project created with Vue CLI:
 vue create my-vue-app
 ```
 
-### For Vue 2.x
 Install the plugin into your project:
 
 ```sh
 cd my-vue-app
 vue add i18n
 ```
 
-### For Vue 3
-
-Install the plugin into your project:
-
-```sh
-cd my-vue-app
-vue add i18n@next
-```
-
 ## :hammer: Injected Commands
 - **`vue-cli-service i18n:report`** (experimental)