gyp: remove from __future__ import with_statement
gyp: remove from __future__ import with_statement

This \_\_future\_\_ import is no longer required in Python >= 2.6.  https://docs.python.org/2/library/__future__.html

PR-URL: https://github.com/nodejs/node-gyp/pull/1799
Reviewed-By: Rod Vagg <f9f03903429036ef609ed7ca822fddfa76155c29@vagg.org>

nodegit/node-gyp,nodejs/node-gyp,nodejs/node-gyp,nodejs/node-gyp,nodegit/node-gyp,nodejs/node-gyp,nodegit/node-gyp,nodejs/node-gyp,nodegit/node-gyp,nodegit/node-gyp