adapt python2 syntax in publish to icecast command

nonstop/management/commands/publish_to_icecast.py

@@ -43,5 +43,5 @@ class Command(BaseCommand):
             try:
                 r = requests.get(stream_url + '&song=' + urllib.quote(onair_msg), timeout=5)
                 r.raise_for_status()
-            except Exception, e:
+            except Exception as e:
                 print('failed to update', e)