Bump puma from 3.12.1 to 3.12.4

Bumps [puma](https://github.com/puma/puma) from 3.12.1 to 3.12.4.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](https://github.com/puma/puma/compare/v3.12.1...v3.12.4)

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

Gemfile

@@ -10,7 +10,7 @@ gem 'rails', '~> 5.2.1'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'
 # Use Puma as the app server
-gem 'puma', '~> 3.11'
+gem 'puma', '~> 3.12'
 # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
 # gem 'jbuilder', '~> 2.5'
 # Use ActiveModel has_secure_password

Gemfile.lock

@@ -133,7 +133,7 @@ GEM
     parser (2.6.5.0)
       ast (~> 2.4.0)
     pg (1.1.4)
-    puma (3.12.1)
+    puma (3.12.4)
     rack (2.0.7)
     rack-cors (1.1.0)
       rack (>= 2.0.0)
@@ -276,7 +276,7 @@ DEPENDENCIES
   listen (>= 3.0.5, < 3.2)
   mailgun-ruby
   pg
-  puma (~> 3.11)
+  puma (~> 3.12)
   rack-cors
   railroady
   rails (~> 5.2.1)