Update jekyll-sitemap to 0.3.0
Update jekyll-sitemap to 0.3.0

Still compatible with Jekyll 1.5.1.
mstred/pages-gem,JustinPatenaude/pages-gem,Stargator/pages-gem,jlord/pages-gem,Stargator/pages-gem,github/pages-gem,github/pages-gem,n060dyz/pages-gem,JustinPatenaude/pages-gem,mstred/pages-gem,jlord/pages-gem,n060dyz/pages-gem