Return output file for GO Term plot.

def get_outfile(self, outfile, goids=None):
        """Return output file for GO Term plot."""
        # 1. Use the user-specfied output filename for the GO Term plot
        if outfile != self.dflt_outfile:
            return outfile
        # 2. If only plotting 1 GO term, use GO is in plot name
        if goids is not None and len(goids) == 1:
            goid = next(iter(goids))
            goobj = self.gosubdag.go2obj[goid]
            fout = "GO_{NN}_{NM}".format(NN=goid.replace("GO:", ""), NM=goobj.name)
            return ".".join([re.sub(r"[\s#'()+,-./:<=>\[\]_}]", '_', fout), 'png'])
        # 3. Return default name
        return self.dflt_outfile