require activesupport < 4.0.0 if RUBY_VERSION < 1.9.3
do not require nokogiri when RUBY_VERSION < 1.9.2 (nokogiri deprecated 1.8)
redcarpet does not support ruby 1.8.7 anymore
allow ruby-head failure
Merge pull request #751 from patriciomacadden/fix-dependencies

Fix test suite