Get the file shebang if is has one.

def shebang(self):
        """Get the file shebang if is has one."""
        with open(self.path, 'rb') as file_handle:
            hashtag = file_handle.read(2)
            if hashtag == b'#!':

                file_handle.seek(0)
                return file_handle.readline().decode('utf8')

        return None