Return the binary of last contract in code.

def compile(cls, code, path=None, libraries=None,
                contract_name='', extra_args=None):
        """ Return the binary of last contract in code. """
        result = cls._code_or_path(
            code,
            path,
            contract_name,
            libraries,
            'bin',
            extra_args)
        return result['bin']