Bug 1294660: Part 4 - Touch clobber file to prevent bustage. r=me

CLOBBER

@@ -22,4 +22,4 @@
 # changes to stick? As of bug 928195, this shouldn't be necessary! Please
 # don't change CLOBBER for WebIDL changes any more.
 
-Bug 1297276 - renaming a file with a different case needed a clobber on case insensitive filesystem
+Bug 1294660 - CSS properties regeneration needs a clobber