Return print format for Grouper, which includes hdr1usr01 and num_usrgos.

def get_prtfmt(self, key="fmta"):
        """Return print format for Grouper, which includes hdr1usr01 and num_usrgos."""
        prtfmt = self.sortobj.grprobj.gosubdag.prt_attr[key]
        prtfmt = prtfmt.replace("{NS}", "{NS} {num_usrgos:>4} uGOs")
        return "".join(['{hdr1usr01:2}', prtfmt, '\n'])