Chore: upgrade ruby and rails versions to run tests against

Drop support for rails 4.2 and 5.0
Drop support for ruby 2.2.x, 2.3.x and 2.4.x

.travis.yml

@@ -1,11 +1,10 @@
 language: ruby
 
 rvm:
-  - 2.2.8
-  - 2.3.5
-  - 2.4.2
+  - 2.5.5
+  - 2.6.3
   - ruby-head
-  - jruby-9.1.9.0
+  - jruby-head
 
 sudo: false
 
@@ -14,13 +13,12 @@ script:
   - bin/rubocop
 
 before_install:
-  - gem install bundler -v 1.16.0
+  - gem install bundler -v 2.0.1
 
 matrix:
   allow_failures:
     - rvm: ruby-head
 
 gemfile:
-  - gemfiles/rails_4.2.gemfile
-  - gemfiles/rails_5.0.gemfile
   - gemfiles/rails_5.1.gemfile
+  - gemfiles/rails_5.2.gemfile

Appraisals

@@ -1,11 +1,7 @@
-appraise "rails-4.2" do
-  gem "rails", "4.2.10"
-end
-
-appraise "rails-5.0" do
-  gem "rails", "5.0.6"
+appraise "rails-5.1" do
+  gem "rails", "5.1.7"
 end
 
-appraise "rails-5.1" do
-  gem "rails", "5.1.4"
+appraise "rails-5.2" do
+  gem "rails", "5.2.3"
 end

gemfiles/rails_5.1.gemfile

@@ -3,6 +3,6 @@
 source "https://rubygems.org"
 
 gem "appraisal", "2.2.0"
-gem "rails", "5.1.4"
+gem "rails", "5.1.7"
 
 gemspec path: "../"

gemfiles/rails_5.0.gemfile → gemfiles/rails_5.2.gemfile

@@ -3,6 +3,6 @@
 source "https://rubygems.org"
 
 gem "appraisal", "2.2.0"
-gem "rails", "5.0.6"
+gem "rails", "5.2.3"
 
 gemspec path: "../"