Bump sitemap_generator from 6.1.2 to 6.3.0

Bumps [sitemap_generator](https://github.com/kjvarga/sitemap_generator) from 6.1.2 to 6.3.0.
- [Changelog](https://github.com/kjvarga/sitemap_generator/blob/master/CHANGES.md)
- [Commits](kjvarga/sitemap_generator@v6.1.2...v6.3.0)

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

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

Gemfile.lock

@@ -408,7 +408,7 @@ GEM
       rack (~> 2.2, >= 2.2.4)
       rack-protection (= 3.1.0)
       tilt (~> 2.0)
-    sitemap_generator (6.1.2)
+    sitemap_generator (6.3.0)
       builder (~> 3.0)
     skylight (6.0.1)
       activesupport (>= 5.2.0)