fix other builds by pinning rest client

Author: JonRowe

Gemfile

@@ -12,6 +12,9 @@ group :documentation do
   gem 'redcarpet',     '2.3.0'
   gem 'github-markup', '1.0.0'
   gem 'relish'
+  if RUBY_VERSION < '2.0.0'
+    gem 'rest-client', '< 2' # dependency of relish
+  end
 end
 
 platforms :jruby do