Bump puma from 3.12.0 to 3.12.4

Bumps [puma](https://github.com/puma/puma) from 3.12.0 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/v3.12.0...v3.12.4)

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

Gemfile

@@ -7,7 +7,7 @@ ruby '2.5.0'
 gem 'rails', '~> 5.2.1'
 
 # 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 Redis adapter to run Action Cable in production

Gemfile.lock

@@ -76,7 +76,7 @@ GEM
     nokogiri (1.8.5)
       mini_portile2 (~> 2.3.0)
     pg (1.1.3)
-    puma (3.12.0)
+    puma (3.12.4)
     rack (2.0.5)
     rack-cors (1.0.2)
     rack-test (1.1.0)
@@ -139,7 +139,7 @@ DEPENDENCIES
   byebug
   listen (>= 3.0.5, < 3.2)
   pg
-  puma (~> 3.11)
+  puma (~> 3.12)
   rack-cors
   rails (~> 5.2.1)
   spring