docs: update install script

dead-horse · dead-horse · commit da84dec7fa16 · 2020-05-17T16:38:38.000+08:00
diff --git a/README.md b/README.md
@@ -23,7 +23,7 @@
 ## Installation
 
 ```bash
-$ npm install @koa/cors@2 --save
+$ npm install @koa/cors --save
 ```
 
 ## Quick start
