Merge pull request #229 from ohbarye/dependabot/bundler/backend/puma-4.3.1

[Security] Bump puma from 4.3.0 to 4.3.1 in /backend

Author: ohbarye

backend/Gemfile.lock

@@ -105,7 +105,7 @@ GEM
       mini_portile2 (~> 2.4.0)
     pg (1.1.4)
     public_suffix (4.0.1)
-    puma (4.3.0)
+    puma (4.3.1)
       nio4r (~> 2.0)
     rack (2.0.7)
     rack-cors (1.0.6)