Fix pyflakes issue.
TOX file.
Switch Travis-CI to use tox.
Guess tox isn't pre-installed on Travis.
Merge remote-tracking branch 'refs/remotes/origin/master' into tox-41
Address review comment: Correct shell escaping.
Address review comment: Even more correct shell escaping.
Add missing dependency.
No need to state dependencies that are already in setup.py.
Merge pull request #43 from hybridcluster/tox-41

Use tox to run tests, pyflakes, sphinx on Travis-CI.

Fixes #41.