Bump proj4 from 2.5.0 to 2.6.0

Bumps [proj4](https://github.com/proj4js/proj4js) from 2.5.0 to 2.6.0.
- [Release notes](https://github.com/proj4js/proj4js/releases)
- [Changelog](https://github.com/proj4js/proj4js/blob/master/changelog.md)
- [Commits](https://github.com/proj4js/proj4js/compare/2.5.0...2.6.0)

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

package.json

@@ -84,7 +84,7 @@
     "ol-mapbox-style": "^5.0.2",
     "pixelmatch": "^5.1.0",
     "pngjs": "^3.4.0",
-    "proj4": "2.5.0",
+    "proj4": "2.6.0",
     "puppeteer": "~1.20.0",
     "rollup": "^1.25.1",
     "rollup-plugin-babel": "^4.3.3",