docs(changelog): add breaking change notice about removal of web animations polyfill

Author: tlancina

CHANGELOG.md

@@ -16,6 +16,11 @@
 
 * **animations:** no longer using Web Animations polyfill ([da18868](https://github.com/driftyco/ionic/commit/da18868))
 
+### Breaking Changes
+
+The Web Animations polyfill is no longer shipped with the framework and may cause build errors.  
+
+Projects will need to be [updated accordingly](https://github.com/driftyco/ionic-conference-app/commit/2ed59e6fd275c4616792c7b2e5aa9da4a20fb188).
 
 <a name="2.0.0-alpha.56"></a>
 # [2.0.0-alpha.56](https://github.com/driftyco/ionic/compare/v2.0.0-alpha.55...v2.0.0-alpha.56) (2016-02-05)