Update sinon.d.ts

I updated sinon to export for RequireJs with a declare statement at the bottom of the document.

sinon/sinon.d.ts

@@ -390,3 +390,7 @@ interface SinonStatic {
 }
 
 declare var sinon: SinonStatic;
+
+declare module "sinon" {
+    export = sinon;
+}