Update issue links to point to sinonjs/sinon
Update issue links to point to sinonjs/sinon

We transferred ownership a while back, and shouldn't make people wait a
full roundtrip to get a redirect from GitHub.

cjohansen/Sinon.JS,mroderick/Sinon.JS,fatso83/Sinon.JS,fatso83/Sinon.JS,fatso83/Sinon.JS,mroderick/Sinon.JS,cjohansen/Sinon.JS,cjohansen/Sinon.JS,mroderick/Sinon.JS