build: bump yell from 2.1.0 to 2.2.0 in /docs

Bumps [yell](https://github.com/rudionrails/yell) from 2.1.0 to 2.2.0.
- [Release notes](https://github.com/rudionrails/yell/releases)
- [Commits](https://github.com/rudionrails/yell/compare/v2.1.0...v2.2.0

)

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

docs/Gemfile.lock

@@ -249,7 +249,7 @@ GEM
     tzinfo (1.2.5)
       thread_safe (~> 0.1)
     unicode-display_width (1.6.0)
-    yell (2.1.0)
+    yell (2.2.0)
 
 PLATFORMS
   ruby