Use puma server & poltergeist Capybara JS driver

Puma is the new default server used by both Rails 5 and Capybara 3 so
using it in all the environments shouldn't hopefully be controversial.

Poltergeist has PhantomJS as a dependency:
https://github.com/teampoltergeist/poltergeist#installing-phantomjs

Gemfile

@@ -20,6 +20,7 @@ gem 'jbuilder', '~> 2.8'
 gem 'mlanett-redis-lock', '0.2.7'
 gem 'plek', '~> 2.1'
 gem 'pg'
+gem 'puma', '~> 3.12.1'
 gem 'rails', '~> 5.2.3'
 gem 'redis-namespace', '1.6.0'
 gem 'sass-rails', '~> 5.0'
@@ -36,6 +37,7 @@ end
 group :development, :test do
   gem 'capybara', '~> 3.10'
   gem 'factory_bot_rails', '~> 4'
+  gem 'poltergeist', '~> 1.18.1'
   gem 'pry-rails'
   gem 'rspec-rails', '~> 3.8'
   gem 'shoulda-matchers', '~> 4.0'

Gemfile.lock

@@ -83,6 +83,7 @@ GEM
       regexp_parser (~> 1.2)
       xpath (~> 3.2)
     chronic (0.10.2)
+    cliver (0.3.2)
     coderay (1.1.2)
     concurrent-ruby (1.1.5)
     crack (0.4.3)
@@ -230,13 +231,18 @@ GEM
       ast (~> 2.4.0)
     pg (1.1.4)
     plek (2.1.1)
+    poltergeist (1.18.1)
+      capybara (>= 2.1, < 4)
+      cliver (~> 0.3.1)
+      websocket-driver (>= 0.2.0)
     powerpack (0.1.2)
     pry (0.12.2)
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
     pry-rails (0.3.9)
       pry (>= 0.10.4)
     public_suffix (3.0.3)
+    puma (3.12.1)
     rack (2.0.7)
     rack-cache (1.9.0)
       rack (>= 0.4)
@@ -423,7 +429,9 @@ DEPENDENCIES
   mlanett-redis-lock (= 0.2.7)
   pg
   plek (~> 2.1)
+  poltergeist (~> 1.18.1)
   pry-rails
+  puma (~> 3.12.1)
   rails (~> 5.2.3)
   redis-namespace (= 1.6.0)
   rspec-rails (~> 3.8)

spec/rails_helper.rb

@@ -10,6 +10,10 @@
 require 'spec_helper'
 require 'rspec/rails'
 require 'capybara/rails'
+require 'capybara/poltergeist'
+
+Capybara.server = :puma, { Silent: true }
+Capybara.javascript_driver = :poltergeist
 
 # Add additional requires below this line. Rails is not loaded until this point!