Bump puma from 3.12.1 to 3.12.6

Bumps [puma](https://github.com/puma/puma) from 3.12.1 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@v3.12.1...v3.12.6)

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

Gemfile

@@ -8,7 +8,7 @@ gem 'rails', '~> 5.2.3'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'
 # Use Puma as the app server
-gem 'puma', '~> 3.11'
+gem 'puma', '~> 3.12'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets

Gemfile.lock

@@ -106,7 +106,7 @@ GEM
       mini_portile2 (~> 2.5.0)
       racc (~> 1.4)
     public_suffix (3.1.0)
-    puma (3.12.1)
+    puma (3.12.6)
     racc (1.5.2)
     rack (2.0.7)
     rack-proxy (0.6.5)
@@ -207,7 +207,7 @@ DEPENDENCIES
   coffee-rails (~> 4.2)
   jbuilder (~> 2.5)
   listen (>= 3.0.5, < 3.2)
-  puma (~> 3.11)
+  puma (~> 3.12)
   rails (~> 5.2.3)
   sass-rails (~> 5.0)
   selenium-webdriver