Changed module_name to repo_name otherwise cookiecutter dies with a KeyError

Cookiecutter relies on the repo_name setting if it was created from a git repo. When trying to create a project from your template by executing:
`cookiecutter  https://github.com/bkonkle/cookiecutter-django.git`

cookiecutter died with the exception below. With module_name replaced by repo_name I could create a project. I assume that this error may not occur when calling cookiecutter with a local template and can see why you prefer module_name over repo_name. So never mind if you reject this pull request.

Traceback (most recent call last):
  File "/usr/local/bin/cookiecutter", line 9, in <module>
    load_entry_point('cookiecutter==0.6.4', 'console_scripts', 'cookiecutter')()
  File "/usr/local/lib/python2.7/dist-packages/cookiecutter/main.py", line 90, in main
    cookiecutter(args.input_dir)
  File "/usr/local/lib/python2.7/dist-packages/cookiecutter/main.py", line 67, in cookiecutter
    generated_project = context['cookiecutter']['repo_name']
KeyError: 'repo_name'