johnson is missing dependencies on the Ruby version

[aspiers]

In this comment in Capybara's issue 3, Steven Parkes said that there are known issues with Johnson on Ruby 1.8.6, but I was able to install it on this version without any warnings or failures. I also see in issue 21 that there are known issues with Johnson on Ruby 1.9.x. Therefore presumably it would make sense to use something like required_ruby_version to hardcode these restrictions into the gem.