Invert the transform

def invert(self):
        """ Invert the transform """
        libfn = utils.get_lib_fn('inverseTransform%s' % (self._libsuffix))
        inv_tx_ptr = libfn(self.pointer)

        new_tx = ANTsTransform(precision=self.precision, dimension=self.dimension,
                                transform_type=self.transform_type, pointer=inv_tx_ptr)

        return new_tx