Update Node libraries that break our Gulp tasks

[jonathanstegall]

Is this update related to a problem? Please describe.
No. The Gulp tasks currently work fine, at least for now.

Current version the plugin includes

• gulp-imagemin 7.1.0
• stylelint 13.13.1

Version to be included

• gulp imagemin 8.0.0
• stylelint 14.1.0

Have you tested this update? What happened?
Yes.

• Imagemin is now a fully ESM package. See this document for more and for some upgrade options.
• Stylelint has breaking changes in version 14. See this document for info about that, and track what gulp-stylelint is doing at this issue: 132