Cap rake and json_pure versions on Ruby < 2.0

Gemfile

@@ -6,8 +6,21 @@ else
   gem 'puppet', :require => false
 end
 
-gem 'puppetlabs_spec_helper', :require => false
+## begin compatibility
+# https://github.com/bundler/bundler/issues/4420
+
 # https://github.com/rspec/rspec-core/issues/1864
-gem 'rspec', '< 3.2.0', {"platforms"=>["ruby_18"]}
-gem 'rspec-puppet', '~> 2.1.0', :require => false
-gem 'metadata-json-lint',       :require => false
+gem 'rspec', '< 3.2.0', :require => false
+
+# rake 11.0+ requires ruby 1.9+
+gem 'rake', '< 11.0.0', :require => false
+
+# json 2.0+ requires ruby 2.0+
+gem 'json', '< 2.0.0',      :require => false
+gem 'json_pure', '< 2.0.0', :require => false
+
+## end compatibility
+
+gem 'puppetlabs_spec_helper', :require => false
+gem 'rspec-puppet',           :require => false
+gem 'metadata-json-lint',     :require => false