Fix a logging message, no bug, r=me

layout/style/nsTransitionManager.cpp

@@ -129,7 +129,7 @@ ElementTransitions::CanPerformOnCompositorThread() const
 {
   if (mElementProperty != nsGkAtoms::transitionsProperty) {
     if (nsLayoutUtils::IsAnimationLoggingEnabled()) {
-      printf_stderr("Gecko bug: Async animation of pseudoelements not supported.  See bug 771367\n");
+      printf_stderr("Gecko bug: Async transition of pseudoelements not supported.  See bug 771367\n");
     }
     return false;
   }