Bump puma from 3.12.1 to 4.3.12

Bumps [puma](https://github.com/puma/puma) from 3.12.1 to 4.3.12.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v3.12.1...v4.3.12)

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

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

Gemfile

@@ -13,7 +13,7 @@ gem 'icalendar', '~> 2.4', '>= 2.4.1'
 gem 'rails', '~> 6.0.1'
 # Use sqlite3 as the database for Active Record
 # 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

@@ -127,7 +127,8 @@ GEM
     pry-gem (1.0.0)
       pry (~> 0.12)
     public_suffix (5.0.0)
-    puma (3.12.6)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     racc (1.6.0)
     rack (2.2.4)
     rack-test (2.0.2)
@@ -221,7 +222,7 @@ DEPENDENCIES
   listen (~> 3.0.5)
   pg
   pry-gem
-  puma (~> 3.0)
+  puma (~> 4.3)
   rails (~> 6.0.1)
   sass-rails (~> 5.0)
   spring