Fix creating of new wiki pages

This breaks because mediawiki doesn't follow their own documented API[1] and doesn't pass
a base revision ID when creating new pages.

Signed-off-by: Patrick Uiterwijk <patrick@puiterwijk.org>

[1]: https://www.mediawiki.org/wiki/Manual:Hooks/PageContentSaveComplete

roles/mediawiki/files/fedmsg-emit.php

@@ -205,7 +205,7 @@ function article_save(
   &$flags,
   $revision,
   &$status,
-  $baseRevId,
+  $baseRevId=0,
   $undidRevId
 ) {