extend travis to test python 3.3 - 3.5

[samuelcolvin]

First of all thanks a lot for pystache, we're using in production and it's great.

Currently .travis.yml only goes up to v3.2 which is now pretty our of date. The readme says pystache is tested on 3.3, but it would also be great if pystache could officially support 3.4 and 3.5.

[samuelcolvin]

Hi @defunkt it looks like pystache needs some love. There are a few old pull requests here and there are some other changes I'd like to propose but there's no point they won't get reviewed.

Would you consider giving pystache a bit of TLC or allowing contributors?

[cclauss]

Add Python 3.6?

[samuelcolvin]

Pretty sure this package is dead. Try https://github.com/noahmorrison/chevron instead.