Bump puma from 3.12.6 to 4.3.8

Bumps [puma](https://github.com/puma/puma) from 3.12.6 to 4.3.8.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](https://github.com/puma/puma/compare/v3.12.6...v4.3.8)

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

Gemfile

@@ -12,7 +12,7 @@ gem 'rails', '~> 5.2.4.3'
 # Use postgresql as the database for Active Record
 gem 'pg', '>= 0.18', '< 2.0'
 # 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

Gemfile.lock

@@ -157,7 +157,8 @@ GEM
       activerecord (>= 5.2.1)
     popper_js (1.14.5)
     public_suffix (3.0.2)
-    puma (3.12.6)
+    puma (4.3.8)
+      nio4r (~> 2.0)
     rack (2.2.3)
     rack-canonical-host (0.2.3)
       addressable (> 0, < 3)
@@ -290,7 +291,7 @@ DEPENDENCIES
   jquery-rails
   listen (>= 3.0.5, < 3.2)
   pg (>= 0.18, < 2.0)
-  puma (~> 3.12)
+  puma (~> 4.3)
   rack-canonical-host
   rails (~> 5.2.4.3)
   recaptcha