Fixed MediaWiki logo in login sprite sheets.
Summary:
I've been advised that that the MediaWiki flower needs to
appear with the square brackets for proper MediaWiki trademark
presentation.
See https://phabricator.wikimedia.org/T543 for relevant discussion.
Test Plan:
view login page with MediaWiki oauth plugin enabled,
see that the logo includes square brackets around the flower
Reviewers: epriestley, qgil, Blessed Reviewers, chad
Reviewed By: Blessed Reviewers, chad
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D10752