Update README.md
Test cleanup for IE8
Merge pull request #136 from mixonic/ie8-tests

Test cleanup for IE8
Allow synchronous detection of transition errors

Needed for https://github.com/emberjs/ember.js/issues/9542
Adding tests
Merge pull request #139 from ef4/sync-err

Allow synchronous detection of transition errors
Merge pull request #135 from rmehlinger/master

Update README.md