Update peep to version 2.0.

This needs to be deleted. 
Once you've run `cookiecutter ...` you should not need to install `peep`.  ...with peep. :)

Perhaps an issue for the near future, but we need to change the docs or something to make it clear to people that they shouldn't do `pip install -r requirements.txt` but instead `./bin/peep.py install -r requirements.txt` or else we miss the whole point of peep. 

Perhaps we should add this to the README in the reference app. What do you think?