Removes maximum Rails version restriction

The gem itself is pretty small and the Rails integration API has been
very stable. Rather than have folks waiting for a version bump for every
minor (or major) release of Rails, it makes more sense to test against
changes proactively and respond to issues when they come up.

.travis.yml

@@ -26,6 +26,10 @@ matrix:
     - rvm: "2.5"
       gemfile: gemfiles/rails42.gemfile
 
+    # Test Rails master against the latest stable version of Ruby
+    - rvm: "ruby"
+      gemfile: gemfiles/rails-master.gemfile
+
   exclude:
     - rvm: "2.3"
       gemfile: Gemfile
@@ -37,6 +41,7 @@ matrix:
       gemfile: gemfiles/rails60.gemfile
   allow_failures:
     - rvm: ruby-head
+    - gemfile: gemfiles/rails-master.gemfile
 
 before_install:
   # Use bundler 1.x with Rails 4.2

gemfiles/rails-master.gemfile

@@ -0,0 +1,11 @@
+source "https://rubygems.org"
+
+gemspec path: ".."
+
+gem "rails", github: "rails/rails"
+
+group :test do
+  gem "aruba"
+  gem "codeclimate-test-reporter", "~> 1.0"
+  gem "rspec"
+end

interactor-rails.gemspec

@@ -15,7 +15,7 @@ Gem::Specification.new do |spec|
   spec.test_files = spec.files.grep(/^spec/)
 
   spec.add_dependency "interactor", "~> 3.0"
-  spec.add_dependency "rails", ">= 4.2", "< 6.1"
+  spec.add_dependency "rails", ">= 4.2"
 
   spec.add_development_dependency "bundler"
   spec.add_development_dependency "rake"