Bump js-yaml and gulp-imagemin in /src/Exceptionless.EmailTemplates (#2037)

Bumps [js-yaml](https://github.com/nodeca/js-yaml) to 3.14.2 and updates ancestor dependency [gulp-imagemin](https://github.com/sindresorhus/gulp-imagemin). These dependencies need to be updated together.


Updates `js-yaml` from 3.13.1 to 3.14.2
- [Changelog](https://github.com/nodeca/js-yaml/blob/master/CHANGELOG.md)
- [Commits](nodeca/js-yaml@3.13.1...3.14.2)

Updates `gulp-imagemin` from 2.4.0 to 9.2.0
- [Release notes](https://github.com/sindresorhus/gulp-imagemin/releases)
- [Commits](sindresorhus/gulp-imagemin@v2.4.0...v9.2.0)

---
updated-dependencies:
- dependency-name: js-yaml
  dependency-version: 3.14.2
  dependency-type: indirect
- dependency-name: gulp-imagemin
  dependency-version: 9.2.0
  dependency-type: direct:development
...

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Author: dependabot[bot]