Merge pull request #298 from ohbarye/dependabot/bundler/backend/rack-2.2.2

[Security] Bump rack from 2.0.8 to 2.2.2 in /backend

Author: ohbarye

backend/Gemfile.lock

@@ -106,7 +106,7 @@ GEM
     public_suffix (4.0.1)
     puma (4.3.3)
       nio4r (~> 2.0)
-    rack (2.0.8)
+    rack (2.2.2)
     rack-cors (1.1.1)
       rack (>= 2.0.0)
     rack-test (1.1.0)