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

traveling-ruby will pre-compile the latest yajl-ruby (1.2.1) and
traveling-bosh will package this. This commit changes the gemspecs
to use yajl-ruby ~> 1.2.0 and minimally updated other vendored gems
Merge pull request #715 from drnic/yajl-ruby-upgrade

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