Bump rack from 2.0.7 to 2.2.3 in /examples/barley

Bumps [rack](https://github.com/rack/rack) from 2.0.7 to 2.2.3.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.7...2.2.3)

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

examples/barley/Gemfile.lock

@@ -33,7 +33,7 @@ GEM
     parslet (1.4.0)
       blankslate (~> 2.0)
     raabro (1.1.6)
-    rack (2.0.7)
+    rack (2.2.3)
     rack-protection (2.0.7)
       rack
     rb-fsevent (0.10.3)