Update Travis link

The current link redirect me to a blank screen in Travis.

```
$ curl -sI https://secure.travis-ci.org/SyrusAkbary/Flask-Super
Admin
HTTP/1.1 301 Moved Permanently
Content-Type: text/html
Location: https://travis-ci.org//SyrusAkbary/Flask-SuperAdmin
Connection: keep-alive
```

That double slash (`//SyrisAkbary`) is wrong. It is probably travis fault (I reported the bug there), but this change solve the problem.