Bump ember-percy from 1.4.0 to 1.6.0

Bumps [ember-percy](https://github.com/percy/ember-percy) from 1.4.0 to 1.6.0.
- [Release notes](https://github.com/percy/ember-percy/releases)
- [Commits](percy/percy-ember@v1.4.0...v1.6.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]