Bump to Jekyll 1.4.2

Only thing of Pages-specific importance is bumping of Maruku to 0.7.0.

[Full release post for v1.4.0](http://jekyllrb.com/news/2013/12/07/jekyll-1-4-0-released/), and the [full history](http://jekyllrb.com/docs/history/#140__20131207)

[Full release post for v1.4.1](http://jekyllrb.com/news/2013/12/10/jekyll-1-4-1-released/), and the [full history](http://jekyllrb.com/docs/history/#141__20131209)

[Full release post for v1.4.2](http://jekyllrb.com/news/2013/12/17/jekyll-1-4-2-released/), and the [full history](http://jekyllrb.com/docs/history/#142__20131217)