Bump puma from 3.12.6 to 4.3.11 in /docs

docs/Gemfile

@@ -11,7 +11,7 @@ gem 'rails', '~> 5.1.4'
 # Use postgresql as the database for Active Record
 gem 'pg', '~> 0.18'
 # 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

docs/Gemfile.lock

@@ -16,8 +16,12 @@ GIT
       slim (>= 3.0, < 5.0)
 
 GEM
-  remote: https://rubygems.org/
   remote: https://rails-assets.org/
+  specs:
+    rails-assets-tether (1.4.7)
+
+GEM
+  remote: https://rubygems.org/
   specs:
     actioncable (5.1.7)
       actionpack (= 5.1.7)
@@ -112,7 +116,8 @@ GEM
       mini_portile2 (~> 2.4.0)
     pg (0.21.0)
     public_suffix (4.0.1)
-    puma (3.12.6)
+    puma (4.3.11)
+      nio4r (~> 2.0)
     rack (2.2.3)
     rack-proxy (0.6.5)
       rack
@@ -130,7 +135,6 @@ GEM
       bundler (>= 1.3.0)
       railties (= 5.1.7)
       sprockets-rails (>= 2.0.0)
-    rails-assets-tether (1.4.7)
     rails-dom-testing (2.0.3)
       activesupport (>= 4.2.0)
       nokogiri (>= 1.6)
@@ -217,7 +221,7 @@ DEPENDENCIES
   listen (>= 3.0.5, < 3.2)
   on-metal!
   pg (~> 0.18)
-  puma (~> 3.12)
+  puma (~> 4.3)
   rails (~> 5.1.4)
   rails-assets-tether!
   redcarpet (~> 3.x)