Add Travis CI and small test

Adds a small test for logins.go , but more importantly adds TravisCI.
manual merge, travis.yml
Merge branch 'catsby-travis'

manual merger of travis.ymlœ
Merge branch 'master' of https://github.com/heroku/force
Auto detect the current endpoint when logging in

Since refresh tokens haven't been implemented yet, I felt it important
to streamline the login process. Rather than always defaulting
`force login` to production, it will instead default it to whatever the
current endpoint is.
Merge pull request #100 from ViViDboarder/smart-login

Auto detect the current endpoint when logging in