Update jekyll to 1.2.0 to solve paginator problem

Using 1.1.2 cause page path problem.

When you visit page 2, the old href link should be {paginate_path}/3 instead of {paginate_path}/2/3.

Update jekyll to latest stable version could solve this problem. :-)
Merge pull request #1378 from librehat/patch-1

Update jekyll to 1.2.0 to solve paginator problem