Bump sdoc from 2.1.0 to 2.2.0

Bumps [sdoc](https://github.com/zzak/sdoc) from 2.1.0 to 2.2.0.
- [Release notes](https://github.com/zzak/sdoc/releases)
- [Changelog](https://github.com/zzak/sdoc/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zzak/sdoc/commits)

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

Gemfile.lock

@@ -225,7 +225,7 @@ GEM
       sprockets (> 3.0)
       sprockets-rails
       tilt
-    sdoc (2.1.0)
+    sdoc (2.2.0)
       rdoc (>= 5.0)
     sprockets (4.0.2)
       concurrent-ruby (~> 1.0)
@@ -287,7 +287,7 @@ DEPENDENCIES
   rails-controller-testing
   rails-i18n (~> 6.0.0)
   sassc-rails (~> 2.1.2)
-  sdoc (~> 2.1.0)
+  sdoc (~> 2.2.0)
   sqlite3 (~> 1.4.1)
   turbolinks (~> 5.2.1)
   tzinfo-data