Upgrade to ember-cli 2.12.3

[notmessenger]

This project uses semver, please check the scope of this pr:

• [ ] #none# - documentation fixes and/or test additions
• [x] #patch# - backwards-compatible bug fix
• [ ] #minor# - adding functionality in a backwards-compatible manner
• [ ] #major# - incompatible API change

CHANGELOG

• Upgrade to ember-cli 2.12.3

[coveralls]

Changes Unknown when pulling d9df1c076a49f47fbc60a9ce305288259105396d on notmessenger:ember-cli-2.12.3 into on ciena-frost:master.

[coveralls]

Changes Unknown when pulling d724c951a412dfffbfc5f49ceba1f495bf8ea857 on notmessenger:ember-cli-2.12.3 into on ciena-frost:master.

[juwara0]

Approved