update 2.12 release notes

notes/2.12.md

@@ -63,7 +63,7 @@ Corresponding issues/pull requests:
 
 The displaying of tiles can now be animated, using CSS3 transitions. Transitions operate on the `opacity` property. Here's the CSS rule defined in OpenLayers' default theme:
 
-    .olTileImage {
+    .olLayerGridTile .olTileImage {
         -webkit-transition: opacity 0.2s linear;
         -moz-transition: opacity 0.2s linear;
         -o-transition: opacity 0.2s linear;
@@ -72,7 +72,7 @@ The displaying of tiles can now be animated, using CSS3 transitions. Transitions
 
 People can override this rule to use other transition settings. To remove tile animation entirely use:
 
-    .olTileImage {
+    .olLayerGridTile .olTileImage {
         -webkit-transition: none;
         -moz-transition: none;
         -o-transition: all 0 none;