chore(deps): bump canvas from 2.7.0 to 2.8.0

Bumps [canvas](https://github.com/Automattic/node-canvas) from 2.7.0 to 2.8.0.
- [Release notes](https://github.com/Automattic/node-canvas/releases)
- [Changelog](https://github.com/Automattic/node-canvas/blob/master/CHANGELOG.md)
- [Commits](Automattic/node-canvas@v2.7.0...v2.8.0)

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