Merge pull request #261 from ohbarye/dependabot/bundler/backend/puma-4.3.3

[Security] Bump puma from 4.3.1 to 4.3.3 in /backend

Author: ohbarye

backend/Gemfile.lock

@@ -104,7 +104,7 @@ GEM
       mini_portile2 (~> 2.4.0)
     pg (1.1.4)
     public_suffix (4.0.1)
-    puma (4.3.1)
+    puma (4.3.3)
       nio4r (~> 2.0)
     rack (2.0.8)
     rack-cors (1.1.1)