Bump proj4 from 2.19.10 to 2.20.0

Bumps [proj4](https://github.com/proj4js/proj4js) from 2.19.10 to 2.20.0.
- [Release notes](https://github.com/proj4js/proj4js/releases)
- [Changelog](https://github.com/proj4js/proj4js/blob/master/changelog.md)
- [Commits](proj4js/proj4js@v2.19.10...v2.20.0)

---
updated-dependencies:
- dependency-name: proj4
  dependency-version: 2.20.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]