Fix linting for python2.7

[gpetrousov]

Currently the linting tests complain about the usage of the 'print' statement as a function.

The command "pytest --mccabe -m mccabe" exited with 1. ... =================================== FAILURES =================================== _________________________ [pylint] git_stalk/stalk.py __________________________ C: 87, 0: Unnecessary parens after 'print' keyword (superfluous-parens) C: 88, 0: Unnecessary parens after 'print' keyword (superfluous-parens) C: 89, 0: Unnecessary parens after 'print' keyword (superfluous-parens) C: 90, 0: Unnecessary parens after 'print' keyword (superfluous-parens) ...

Suggestion(s):

• We need to fix this by adjust either travis file to use environments
• Import future print function as suggested here
  https://stackoverflow.com/questions/28694380/pylint-says-unnecessary-parens-after-r-keyword