Update ember-frost-notifier

[dafortin]

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

• [x] #patch# - backwards-compatible bug fix
• [ ] #minor# - adding functionality in a backwards-compatible manner
• [ ] #major# - incompatible API change

Note: it's a minor because ember-frost-notifier is only used in the demo.

CHANGELOG

• Updated ember-frost-notifier to ^4.0.0

[quincyle]

Approved