Fix missing .gitignore file

By default, npm skips certain files when installing a package.
See https://www.npmjs.org/doc/developers.html for details.

This behavior causes the generator to crash when trying to copy
the '.gitignore' file contained in the 'templates' folder
because npm skipped this file when downloading the package.
Merge pull request #1 from ahelmberger/fix-gitignore

Fix missing .gitignore file