Bump puma from 3.7.1 to 4.3.9 in /examples/rails5_app

Bumps [puma](https://github.com/puma/puma) from 3.7.1 to 4.3.9.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v3.7.1...v4.3.9)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

examples/rails5_app/Gemfile

@@ -11,7 +11,7 @@ gem 'rails', '~> 5.0.2'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'
 # Use Puma as the app server
-gem 'puma', '~> 3.0'
+gem 'puma', '~> 4.3'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets

examples/rails5_app/Gemfile.lock

@@ -89,7 +89,8 @@ GEM
       mini_portile2 (~> 2.7.0)
       racc (~> 1.4)
     orm_adapter (0.5.0)
-    puma (3.7.1)
+    puma (4.3.9)
+      nio4r (~> 2.0)
     racc (1.6.0)
     rack (2.0.7)
     rack-test (0.6.3)
@@ -176,7 +177,7 @@ DEPENDENCIES
   jbuilder (~> 2.5)
   jquery-rails
   listen (~> 3.0.5)
-  puma (~> 3.0)
+  puma (~> 4.3)
   rails (~> 5.0.2)
   sass-rails (~> 5.0)
   spring