Improve Travis CI matrix

- Test against latest Ubuntu LTS (20.04)
- Test against latest Ruby versions
- Test against Rails Edge and Ruby Head to discover failures in advance

.travis.yml

@@ -1,3 +1,5 @@
+dist: focal
+os: linux
 language: ruby
 before_install: gem install bundler
 cache: bundler
@@ -8,9 +10,36 @@ gemfile:
   - gemfiles/rails_5_2.gemfile
   - gemfiles/rails_6_0.gemfile
   - gemfiles/rails_6_1.gemfile
+  - gemfiles/rails_edge.gemfile
 
 rvm:
-  - "2.5.3"
+  - "2.5.8"
+  - "2.6.6"
+  - "2.7.2"
+  - ruby-head
+
+jobs:
+  allow_failures:
+    - rvm: ruby-head
+    - gemfile: gemfiles/rails_edge.gemfile
+  exclude:
+    - rvm: 2.5.8
+      gemfile: gemfiles/rails_edge.gemfile
+    - rvm: 2.6.6
+      gemfile: gemfiles/rails_edge.gemfile
+    - rvm: 2.7.2
+      gemfile: gemfiles/rails_5_0.gemfile
+    - rvm: 2.7.2
+      gemfile: gemfiles/rails_5_1.gemfile
+    - rvm: 2.7.2
+      gemfile: gemfiles/rails_5_2.gemfile
+    - rvm: ruby-head
+      gemfile: gemfiles/rails_5_0.gemfile
+    - rvm: ruby-head
+      gemfile: gemfiles/rails_5_1.gemfile
+    - rvm: ruby-head
+      gemfile: gemfiles/rails_5_2.gemfile
+  fast_finish: true
 
 script: 'bundle exec rspec'
 

Appraisals

@@ -18,3 +18,7 @@ end
 appraise "rails_6_1" do
   gem "rails", "~> 6.1.0"
 end
+
+appraise "rails_edge" do
+  gem "rails", git: "https://github.com/rails/rails.git", branch: "main"
+end

gemfiles/rails_edge.gemfile

@@ -0,0 +1,14 @@
+# This file was generated by Appraisal
+
+source "http://rubygems.org"
+
+gem "rails", git: "https://github.com/rails/rails.git", branch: "main"
+gem "rspec"
+gem "rspec-rails", "~> 3.7"
+gem "sqlite3"
+gem "timecop"
+gem "byebug"
+gem "appraisal"
+gem "nokogiri", "~> 1.8"
+
+gemspec path: "../"