Bump rack from 2.2.11 to 2.2.12 (#243)

Author: dependabot[bot]

Gemfile.lock

@@ -339,7 +339,7 @@ GEM
       json
       websocket (~> 1.0)
     racc (1.8.1)
-    rack (2.2.11)
+    rack (2.2.12)
     rack-protection (3.2.0)
       base64 (>= 0.1.0)
       rack (~> 2.2, >= 2.2.4)