Plot GO IDs.

def _plt_gosubdag(self, goids, go2color, **kws):
        """Plot GO IDs."""
        fout_img = self.get_outfile(kws['outfile'], goids)
        objcolor = Go2Color(self.gosubdag, objgoea=None, go2color=go2color)
        objplt = GoSubDagPlot(self.gosubdag, Go2Color=objcolor, **kws)
        objplt.prt_goids(sys.stdout)
        objplt.plt_dag(fout_img)
        return fout_img