Update puma to version 4.2.1

Author: depfu[bot]

Gemfile

@@ -11,7 +11,7 @@ gem 'rails', '~> 5.1.1'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'
 # Use Puma as the app server
-gem 'puma', '~> 3.7'
+gem 'puma', '~> 4.2'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets

Gemfile.lock

@@ -90,7 +90,8 @@ GEM
     nokogiri (1.10.1)
       mini_portile2 (~> 2.4.0)
     public_suffix (3.0.2)
-    puma (3.9.1)
+    puma (4.2.1)
+      nio4r (~> 2.0)
     rack (2.0.7)
     rack-protection (2.0.7)
       rack
@@ -189,7 +190,7 @@ DEPENDENCIES
   coffee-rails (~> 4.2)
   jbuilder (~> 2.5)
   listen (>= 3.0.5, <= 3.2.0)
-  puma (~> 3.7)
+  puma (~> 4.2)
   rails (~> 5.1.1)
   sass-rails (~> 5.0)
   selenium-webdriver