Added <if __name__ == '__main__'> to avoid RuntimeError

[CarettaCaretta11]

Wasn't able to train DualGAN on Mac as the following error was raised

RuntimeError: 
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

        This probably means that you are not using fork to start your
        child processes and you have forgotten to use the proper idiom
        in the main module:

            if __name__ == '__main__':
                freeze_support()
                ...

        The "freeze_support()" line can be omitted if the program
        is not going to be frozen to produce an executable.

        To fix this issue, refer to the "Safe importing of main module"
        section in https://docs.python.org/3/library/multiprocessing.html

Using if __name__ == "main" appears to have solved my problem.

[baicaiPCX]

您好，您的邮件小皮已经收到啦！！！