use os.path.join for config_file_name

pyfstat/make_sfts.py

@@ -96,7 +96,7 @@ class Writer(BaseSearchClass):
             os.makedirs(self.outdir)
         if self.tref is None:
             self.tref = self.tstart
-        self.config_file_name = "{}/{}.cff".format(self.outdir, self.label)
+        self.config_file_name = os.path.join(self.outdir,self.label+".cff")
         self.sftfilenames = [
             lalpulsar.OfficialSFTFilename(
                 dets[0],