Add python2 to build matrix
travis already sets the TRAVIS environment variable
Sort Python versions
clarify the TRAVIS conditional in the makefile
Revert "clarify the TRAVIS conditional in the makefile"

This reverts commit 702d082180925f46b5d298f0e245ae23ffd1eff9.
fix conflicts with master
Merge pull request #40 from jacebrowning/python2

Add python2 to build matrix