Support Jekyll >1.0 flags in Makefile

Jekyll changed the names of it's flags & syntax for serving the site with the 1.0 release. This change means the Makefile will check and use the appropriate syntax.
Merge pull request #1 from exo/master

Support Jekyll 1.0 syntax.

exo added flags to the Makefile that correctly set flags for <1 and >1 versions of Jekyll.

We think.