travis: Add Rails 6.1

.travis.yml

@@ -14,6 +14,7 @@ gemfile:
   - test/gemfiles/rails_5_0.gemfile
   - test/gemfiles/rails_5_1.gemfile
   - test/gemfiles/rails_6_0.gemfile
+  - test/gemfiles/rails_6_1.gemfile
 
 jobs:
   exclude:

test/gemfiles/rails_6_1.gemfile

@@ -0,0 +1,7 @@
+source 'https://rubygems.org'
+
+gem 'actionpack', '~> 6.1.3'
+gem 'activesupport', '~> 6.1.3'
+gem 'autoprefixer-rails', '>= 9.7.6'
+
+gemspec path: '../../'