Update version of safe_yaml to ~> 0.9.7 to be compatible with Jekyll v1.3

https://github.com/mojombo/jekyll/issues/1685
Force use of Jekyll 1.3.0 <= x < 2.0.0
Merge pull request #65 from jekyll/update-safe_yaml-dep

Update version of safe_yaml to ~> 0.9.7 to be compatible with Jekyll v1.3