Bump puma from 3.12.0 to 4.3.8

Bumps [puma](https://github.com/puma/puma) from 3.12.0 to 4.3.8. - [Release notes](https://github.com/puma/puma/releases) - [Changelog](https://github.com/puma/puma/blob/master/History.md) - [Commits](puma/puma@v3.12.0...v4.3.8) Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Gemfile

@@ -12,7 +12,7 @@ gem 'rails', '~> 5.1.4'
 # Use mysql as the database for Active Record
 gem 'mysql2', '>= 0.3.18', '< 0.5'
 # Use Puma as the app server
-gem 'puma', '~> 3.7'
+gem 'puma', '~> 4.3'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets

Gemfile.lock

@@ -100,7 +100,8 @@ GEM
  mini_portile2 (~> 2.4.0)
  orm_adapter (0.5.0)
  public_suffix (3.0.3)
- puma (3.12.0)
+ puma (4.3.8)
+ nio4r (~> 2.0)
  rack (2.0.6)
  rack-test (1.1.0)
  rack (>= 1.0, < 3)
@@ -197,7 +198,7 @@ DEPENDENCIES
  jbuilder (~> 2.5)
  listen (>= 3.0.5, < 3.2)
  mysql2 (>= 0.3.18, < 0.5)
- puma (~> 3.7)
+ puma (~> 4.3)
  rails (~> 5.1.4)
  sass-rails (~> 5.0)
  selenium-webdriver