Bump puma from 3.9.1 to 3.12.6

Bumps [puma](https://github.com/puma/puma) from 3.9.1 to 3.12.6.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v3.9.1...v3.12.6)

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

Gemfile

@@ -11,7 +11,7 @@ gem 'rails', '~> 6.1'
 # Use postgresql as the database for Active Record
 gem 'pg', '~> 0.18'
 # Use Puma as the app server
-gem 'puma', '~> 3.7'
+gem 'puma', '~> 3.12'
 # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
 # gem 'jbuilder', '~> 2.5'
 # Use Redis adapter to run Action Cable in production

Gemfile.lock

@@ -97,7 +97,7 @@ GEM
       mini_portile2 (~> 2.5.0)
       racc (~> 1.4)
     pg (0.20.0)
-    puma (3.9.1)
+    puma (3.12.6)
     racc (1.5.2)
     rack (2.2.3)
     rack-test (1.1.0)
@@ -178,7 +178,7 @@ DEPENDENCIES
   factory_girl_rails
   listen (>= 3.0.5, < 3.2)
   pg (~> 0.18)
-  puma (~> 3.7)
+  puma (~> 3.12)
   rails (~> 6.1)
   rspec-rails (~> 3.6)
   spring