Bump puma from 3.12.6 to 4.3.11 in /examples/rails_app

Bumps [puma](https://github.com/puma/puma) from 3.12.6 to 4.3.11.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v3.12.6...v4.3.11)

---
updated-dependencies:
- dependency-name: puma
  dependency-type: direct:production
...

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', '~> 3.12'
+gem 'puma', '~> 4.3'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets

examples/rails_app/Gemfile.lock

@@ -96,7 +96,9 @@ GEM
     marcel (0.3.3)
       mimemagic (~> 0.3.2)
     method_source (0.9.2)
-    mimemagic (0.3.3)
+    mimemagic (0.3.10)
+      nokogiri (~> 1)
+      rake
     mini_mime (1.0.1)
     mini_portile2 (2.4.0)
     minitest (5.11.3)
@@ -105,7 +107,8 @@ GEM
     nokogiri (1.10.4)
       mini_portile2 (~> 2.4.0)
     public_suffix (3.0.3)
-    puma (3.12.6)
+    puma (4.3.11)
+      nio4r (~> 2.0)
     rack (2.2.3)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
@@ -205,7 +208,7 @@ DEPENDENCIES
   jbuilder (~> 2.5)
   listen (>= 3.0.5, < 3.2)
   nokogiri (~> 1.10)
-  puma (~> 3.12)
+  puma (~> 4.3)
   rails (~> 5.2.0)
   sass-rails (~> 5.0)
   selenium-webdriver