Upgrade ember-cli to 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 ember-cli to 2.12.3

[juwara0]

Approved

[coveralls]

Changes Unknown when pulling d438238936f26b255f884e41f3513a578dbe61a5 on notmessenger:ember-cli-2.12.3 into on ciena-frost:master.

[juwara0]

Approved