Update gulp-imagemin to the latest version 🚀

[greenkeeper]

The devDependency gulp-imagemin was updated from 5.0.3 to 6.0.0.

This version is not covered by your current version range.

If you don’t accept this pull request, your project will work just like it did before. However, you might be missing out on a bunch of new features, fixes and/or performance improvements from the dependency update.

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Release Notes for v6.0.0

Breaking:

• Require Node.js 8 6e091ed

v5.0.3...v6.0.0

Commits

The new version differs by 3 commits.

• 97cd1c3 6.0.0
• 6e091ed Require Node.js 8
• c1c3346 Create funding.yml

See the full diff

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