Execute the command.

def run(self):
        """ Execute the command.

        """
        args = {"remote": self.remote, "branch": self.branch}
        cmdl = "git pull --ff-only {remote:s} {branch:s}".format(**args)
        try:
            check_call(cmdl.split())
        except CalledProcessError:
            raise SystemExit(1)
        log.info("package version is now {:s}".format(version()))
        return