[fixes #1265] don’t diverge the promise chains (we must wait for the update to occur)

tests + refactoring
Add UpdateTask test to check if package.json file gets updated with new version number
Merge pull request #1273 from andycrum/fix-ember-update-task

Add UpdateTask test to check if package.json file gets updated with new version number
Merge pull request #1266 from stefanpenner/fix-ember-updatae

[fixes #1265] don’t diverge the promise chain (we must wait for the upda...