Use pip to freeze the requirements and save them to the local
        requirements.txt file.

def freeze(self):
        '''
        Use pip to freeze the requirements and save them to the local
        requirements.txt file.
        '''
        remote_path = os.path.join(self.venv, 'requirements.txt')
        run('{} freeze > {}'.format(self.pip(), remote_path))
        get(remote_path, self.requirements)