fix readme bug

Author: nuo.xun

README.md

@@ -41,7 +41,7 @@ After installed gitbook.
 
 ```
     > git clone [email protected]:gitbook-plugins/gitbook-plugin-search-pro.git -b gh-pages
-    > cd ./gitbook-plugin-search-pro.git
+    > cd ./gitbook-plugin-search-pro
     > npm install
     > gitbook serve ./
 ```