Fix writing catalog csv on Windows (#235)

on Windows, `csep.catalogs.AbstractBaseCatalog.write_ascii()` interleaved every entry with an empty line

see also: https://stackoverflow.com/a/3348664

csep/core/catalogs.py

@@ -325,7 +325,7 @@ def write_ascii(self, filename, write_header=True, write_empty=True, append=Fals
             write_string = 'a'
         else:
             write_string = 'w'
-        with open(filename, write_string) as outfile:
+        with open(filename, write_string, newline='') as outfile:
             writer = csv.DictWriter(outfile, fieldnames=header, delimiter=',')
             if write_header:
                 writer.writeheader()