Do not use VizierList for -out

Author: jwoillez

astroquery/vizier/core.py

@@ -576,7 +576,7 @@ def _args_to_payload(self, *args, **kwargs):
         if columns_default:
             body['-out'] = '*'
         else:
-            body['-out'] = columns_out
+            body['-out'] = ','.join(columns_out)
 
         if columns_out:
             body['-out.add'] = ','.join(columns_out)