Update readme about the version of gin (#1494)

README.md

@@ -100,7 +100,7 @@ $ mkdir -p $GOPATH/src/github.com/myusername/project && cd "$_"
 
 ```sh
 $ govendor init
-$ govendor fetch github.com/gin-gonic/gin@v1.2
+$ govendor fetch github.com/gin-gonic/gin@v1.3
 ```
 
 4. Copy a starting template inside your project