Fetch env from git repo

Add the following to Capistrano (`Capfile`): 

    set :environment_repository, 'git@git.example.com:path/to/your_repo.git'

    # This line is optional - if you're using '.my_own_file' instead of '.env'
    set :environment_file, '.my_own_file'

Note that you may have to setup key forwarding on your local machine, and add your keys to your Git host (i.e. add your keys to your github.com account - or whomever you use for a git host)