Bump jekyll from 4.2.0 to 4.2.1 in /docs (#721)

Bumps [jekyll](https://github.com/jekyll/jekyll) from 4.2.0 to 4.2.1.
- [Release notes](https://github.com/jekyll/jekyll/releases)
- [Changelog](https://github.com/jekyll/jekyll/blob/master/History.markdown)
- [Commits](https://github.com/jekyll/jekyll/compare/v4.2.0...v4.2.1)

---
updated-dependencies:
- dependency-name: jekyll
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/Gemfile.lock

@@ -4,17 +4,17 @@ GEM
     addressable (2.8.0)
       public_suffix (>= 2.0.2, < 5.0)
     colorator (1.1.0)
-    concurrent-ruby (1.1.7)
+    concurrent-ruby (1.1.9)
     em-websocket (0.5.2)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.6.0)
     eventmachine (1.2.7)
-    ffi (1.14.2)
+    ffi (1.15.4)
     forwardable-extended (2.6.0)
     http_parser.rb (0.6.0)
-    i18n (1.8.5)
+    i18n (1.8.10)
       concurrent-ruby (~> 1.0)
-    jekyll (4.2.0)
+    jekyll (4.2.1)
       addressable (~> 2.4)
       colorator (~> 1.0)
       em-websocket (~> 0.5)
@@ -40,24 +40,24 @@ GEM
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
     liquid (4.0.3)
-    listen (3.3.3)
+    listen (3.7.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     mercenary (0.4.0)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
     public_suffix (4.0.6)
-    rb-fsevent (0.10.4)
+    rb-fsevent (0.11.0)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     rexml (3.2.5)
-    rouge (3.26.0)
+    rouge (3.26.1)
     safe_yaml (1.0.5)
     sassc (2.4.0)
       ffi (~> 1.9)
     terminal-table (2.0.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
-    unicode-display_width (1.7.0)
+    unicode-display_width (1.8.0)
 
 PLATFORMS
   x86_64-linux