build(deps): bump proj4 from 2.12.1 to 2.15.0

Bumps [proj4](https://github.com/proj4js/proj4js) from 2.12.1 to 2.15.0.
- [Release notes](https://github.com/proj4js/proj4js/releases)
- [Changelog](https://github.com/proj4js/proj4js/blob/master/changelog.md)
- [Commits](proj4js/proj4js@v2.12.1...v2.15.0)

---
updated-dependencies:
- dependency-name: proj4
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]