Bump sitemap_generator from 5.3.1 to 6.0.2

Bumps [sitemap_generator](https://github.com/kjvarga/sitemap_generator) from 5.3.1 to 6.0.2.
- [Release notes](https://github.com/kjvarga/sitemap_generator/releases)
- [Changelog](https://github.com/kjvarga/sitemap_generator/blob/master/CHANGES.md)
- [Commits](kjvarga/sitemap_generator@v5.3.1...v6.0.2)

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

Gemfile

@@ -13,7 +13,7 @@ gem 'share_notify', git: 'https://github.com/samvera-labs/share_notify', branch:
 #gem 'solrizer-fedora', '3.0.0.pre1' # PRE-LOCK
 gem "solrizer-fedora", git: 'https://github.com/ucsdlib/solrizer-fedora', ref: '87c2d35e'
 
-gem 'sitemap_generator', '~> 5.3.1'
+gem 'sitemap_generator', '~> 6.0.2'
 
 gem 'pg', '~> 0.18.2'
 gem 'activerecord-postgresql-adapter'

Gemfile.lock

@@ -382,7 +382,7 @@ GEM
       json (>= 1.8, < 3)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.0)
-    sitemap_generator (5.3.1)
+    sitemap_generator (6.0.2)
       builder (~> 3.0)
     slop (3.6.0)
     solrizer (3.1.1)
@@ -485,7 +485,7 @@ DEPENDENCIES
   selenium-webdriver (= 3.4.0)
   share_notify!
   simplecov (~> 0.14.1)
-  sitemap_generator (~> 5.3.1)
+  sitemap_generator (~> 6.0.2)
   solrizer (~> 3.1.0)
   solrizer-fedora!
   sprockets (~> 2.12.4)