Fix broken link to CONTRIBUTING.md
Fix broken link to CONTRIBUTING.md

Thanks to @drook for reporting it via #2033
sass/node-sass,nschonni/node-sass,sass/node-sass,xzyfer/node-sass,saper/node-sass,nschonni/node-sass,xzyfer/node-sass,sass/node-sass,saper/node-sass,saper/node-sass,nschonni/node-sass,sass/node-sass,saper/node-sass,xzyfer/node-sass,nschonni/node-sass,xzyfer/node-sass,sass/node-sass,sass/node-sass,saper/node-sass,nschonni/node-sass,xzyfer/node-sass,xzyfer/node-sass,sass/node-sass,nschonni/node-sass,saper/node-sass,saper/node-sass,xzyfer/node-sass,nschonni/node-sass