Update homepage
Update homepage

Current homepage points to an expired domain http://getsprockets.org

This PR updates it to point at the github repo instead.

guilleiguaran/sprockets,eileencodes/sprockets,sideci-sample/sideci-sample-sprockets,prathamesh-sonpatki/sprockets,Andreis13/sprockets,byroot/sprockets,masarakki/sprockets,tricknotes/sprockets,jcoyne/sprockets,rails/sprockets,bdezonia/sprockets,kappezoro/sprockets,prusswan/sprockets,jeremy/sprockets,sferik/sprockets,basecamp/sprockets,maclover7/sprockets,daniel-rikowski/sprockets,askl56/sprockets,JuanitoFatas/sprockets,orlando/sprockets,recursecenter/sprockets