do not specify python version for docs env in tox settings

Author: dhellmann

tox.ini

@@ -31,7 +31,6 @@ setenv =
 commands =  ksh ./tests/run_tests {envdir} []
 
 [testenv:docs]
-basepython=python2.7
 deps =
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/docs/requirements.txt