Upgrade to latest yajl-ruby towards support for traveling-ruby

traveling-ruby will pre-compile the latest yajl-ruby (1.2.1) and https://github.com/cloudfoundry-community/traveling-bosh will package this. This commit changes the gemspecs to use yajl-ruby ~> 1.2.0 and minimally updated other vendored gems

https://github.com/phusion/traveling-ruby/issues/6#issuecomment-67272455