Require Python >= 2.7.
Require Python >= 2.7.

This is due to the use of `re.sub` with the `flags` argument (used as
part of the join feature).

As per the Python docs [1]:

    re.sub(pattern, repl, string, count=0, flags=0)

    ...snip...

    Changed in version 2.7: Added the optional flags argument.

[1]: https://docs.python.org/2/library/re.html

mjrusso/mountain