Bump rack from 2.1.2 to 2.2.3 in /builder

Bumps [rack](https://github.com/rack/rack) from 2.1.2 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@2.1.2...2.2.3)

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

Author: dependabot[bot]

builder/Gemfile.lock

@@ -87,7 +87,7 @@ GEM
     nokogiri (1.10.8)
       mini_portile2 (~> 2.4.0)
     puma (3.12.4)
-    rack (2.1.2)
+    rack (2.2.3)
     rack-proxy (0.6.5)
       rack
     rack-test (1.1.0)