Works with PyJWT 0.4.x (also unpinned). Contributions by (Wichert Akkerman
<wichertwiggy.net>) that enable the auth to use a 'Bearer' header rather than
the custom header 'JWT'.
Dropped support for Python 3.3 in tox, but it should still work fine.
Addition (from development) perspective of using Vagrant to develop and
tox-test the package against python 2.7 and 3.4