travis: Fix push to GitHub
travis: Fix push to GitHub

Commit 9cdc4257 (travis: Fail build if unable to push to DockerHub)
moved the logic for pushing the dev tag to GitHub from the
`after_success` target to `deploy`. For some reason, this resulted in
the following error:
```
remote: Not Found
fatal: repository 'https://[secure]@github.com/kelda/kelda/' not found
```

Adding `.git` to the repository URL fixes this error.

kelda/kelda,LuiseV/quilt,kelda/kelda,NetSys/quilt,LuiseV/quilt,LuiseV/quilt,quilt/quilt,NetSys/quilt,LuiseV/quilt,quilt/quilt,NetSys/quilt,LuiseV/quilt,NetSys/quilt,kelda/kelda,kelda/kelda,quilt/quilt,quilt/quilt,NetSys/quilt