Ensure we're inside a virtualenv.

def check_venv(self):
        """ Ensure we're inside a virtualenv. """
        if self.zappa:
            venv = self.zappa.get_current_venv()
        else:
            # Just for `init`, when we don't have settings yet.
            venv = Zappa.get_current_venv()
        if not venv:
            raise ClickException(
                click.style("Zappa", bold=True) + " requires an " + click.style("active virtual environment", bold=True, fg="red") + "!\n" +
                "Learn more about virtual environments here: " + click.style("http://docs.python-guide.org/en/latest/dev/virtualenvs/", bold=False, fg="cyan"))