Bump puma from 3.12.0 to 3.12.6

Bumps [puma](https://github.com/puma/puma) from 3.12.0 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@v3.12.0...v3.12.6)

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

Gemfile

@@ -8,7 +8,7 @@ gem 'rails', '~> 5.2.1'
 # Use postgresql as the database for Active Record
 gem 'pg', '>= 0.18', '< 2.0'
 # Use Puma as the app server
-gem 'puma', '~> 3.11'
+gem 'puma', '~> 3.12'
 # Transpile app-like JavaScript. Read more: https://github.com/rails/webpacker
 gem 'webpacker'
 # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder

Gemfile.lock

@@ -91,7 +91,7 @@ GEM
       mini_portile2 (~> 2.5.0)
       racc (~> 1.4)
     pg (1.1.4)
-    puma (3.12.0)
+    puma (3.12.6)
     racc (1.5.2)
     rack (2.2.3)
     rack-proxy (0.6.5)
@@ -187,7 +187,7 @@ DEPENDENCIES
   jbuilder (~> 2.5)
   listen (>= 3.0.5, < 3.2)
   pg (>= 0.18, < 2.0)
-  puma (~> 3.11)
+  puma (~> 3.12)
   rails (~> 5.2.1)
   rspec-rails (~> 3.5)
   shoulda-matchers (~> 3.1)