Add link to Travis CI page

README.md

@@ -1,5 +1,5 @@
 ![vim-plug](https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.png)
-![travis-ci](https://travis-ci.org/junegunn/vim-plug.svg?branch=master)
+[![travis-ci](https://travis-ci.org/junegunn/vim-plug.svg?branch=master)](https://travis-ci.org/junegunn/vim-plug)
 
 A minimalist Vim plugin manager.