Bump puma from 3.12.1 to 3.12.6 in /examples/rails_app

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](https://github.com/puma/puma/commits)

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

Author: dependabot[bot]

examples/rails_app/Gemfile

@@ -8,7 +8,7 @@ gem 'rails', '~> 5.2.0'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3', '~> 1.3.6'
 # 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

examples/rails_app/Gemfile.lock

@@ -105,7 +105,7 @@ GEM
     nokogiri (1.10.4)
       mini_portile2 (~> 2.4.0)
     public_suffix (3.0.3)
-    puma (3.12.1)
+    puma (3.12.6)
     rack (2.2.3)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
@@ -205,7 +205,7 @@ DEPENDENCIES
   jbuilder (~> 2.5)
   listen (>= 3.0.5, < 3.2)
   nokogiri (~> 1.10)
-  puma (~> 3.11)
+  puma (~> 3.12)
   rails (~> 5.2.0)
   sass-rails (~> 5.0)
   selenium-webdriver