Bump puma from 3.9.1 to 4.3.8

Bumps [puma](https://github.com/puma/puma) from 3.9.1 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@v3.9.1...v4.3.8)

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

Gemfile

@@ -15,7 +15,7 @@ gem 'materialize-form'
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem 'rails', '~> 5.0.2'
 # 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

Gemfile.lock

@@ -101,7 +101,8 @@ GEM
     nokogiri (1.12.5-x64-mingw32)
       racc (~> 1.4)
     orm_adapter (0.5.0)
-    puma (3.9.1)
+    puma (4.3.8)
+      nio4r (~> 2.0)
     racc (1.5.2)
     rack (2.2.3)
     rack-test (0.6.3)
@@ -207,7 +208,7 @@ DEPENDENCIES
   material_icons
   materialize-form
   materialize-sass
-  puma (~> 3.0)
+  puma (~> 4.3)
   rails (~> 5.0.2)
   rails-ujs
   rails_12factor