Pin rake on older Ruby

Author: JonRowe

Gemfile

@@ -16,8 +16,10 @@ if RUBY_VERSION < '1.9.3'
   gem 'rake', '< 11.0.0' # rake 11 requires Ruby 1.9.3 or later
 elsif RUBY_VERSION < '2.0.0'
   gem 'rake', '< 12.0.0' # rake 12 requires Ruby 2.0.0 or later
+elsif RUBY_VERSION < '2.2.0'
+  gem 'rake', '< 13.0.0' # rake 13 requires Ruby 2.2.0 or later
 else
-  gem 'rake', '>= 12.3.3'
+  gem 'rake', '>= 13.0.0'
 end
 
 if ENV['DIFF_LCS_VERSION']