Add changelog for 3.1.0
Add changelog for 3.1.0

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