Revert "travis: try and enable python 2.7"
Revert "travis: try and enable python 2.7"

This reverts commit 2afc4296f852a17254bf2a4689bf5ef765032ab5.

danielhkl/matplotlib2tikz,dougnd/matplotlib2tikz,nschloe/matplotlib2tikz,m-rossi/matplotlib2tikz