Documentation updates + .travis.yml fix

[dhaynespls]

closes #8

added:

• python 3 specified on README's
• " " on .travis.yml

[dhaynespls]

Interesting --

https://travis-ci.org/michalczaplinski/pitchfork/jobs/187941425

vs.

https://travis-ci.org/bruno207/pitchfork/jobs/187940544

I'm not sure why it worked on my build and not yours. ¯_(ツ)_/¯

[fortes]

Closing this since travis is now running again!