Merge pull request #2664 from rspec/fix-build-by-pinning-minitest

Pin minitest on older Rubies

Author: JonRowe

Gemfile

@@ -64,6 +64,12 @@ end
 
 gem 'test-unit', '~> 3.0' if RUBY_VERSION.to_f >= 2.2
 
+# Version 5.12 of minitest requires Ruby 2.4
+if RUBY_VERSION < '2.4.0'
+  gem 'minitest', '< 5.12.0'
+end
+
+
 gem 'contracts', '< 0.16' if RUBY_VERSION < '1.9.0'
 
 eval File.read('Gemfile-custom') if File.exist?('Gemfile-custom')