tox.ini: Bring over changes from 1.0-alpha branch

These are the changes that @sigmavirus24 did to `tox.ini` on the
`1.0-alpha` branch in
https://github.com/sigmavirus24/github3.py/pull/287
.travis.yml: Bring over changes from 1.0-alpha branch

These are the changes that @sigmavirus24 did to `.travis.yml` on the
`1.0-alpha` branch in sigmavirus24#287
Merge pull request #293 from msabramo/bring_tox.ini_from_1.0-alpha_branch

tox.ini: Bring over changes from 1.0-alpha branch