Explicitly call Python2 to run gyp on Linux. Python usually refers to the latest version. If there is version 3 installed, it resolves to the the Python 3 interpreter. This change ensures that Python 2 is used. There is no need to install gyp on a Linux machines anymore.
Merge pull request #341 from adobe/irichter/linux-run-gyp-with-python2

Explicitly call Python2 to run gyp on Linux.