Add onCall(n) and friends to SinonStub definition

These were added in Sinon 1.8, and the definition claims to be Sinon
1.8.1

From documentation:
"As of Sinon version 1.8, you can use the onCall method to make a stub
respond differently on consecutive calls."

http://sinonjs.org/docs/

sinon/sinon.d.ts

@@ -101,6 +101,10 @@ interface SinonStub extends SinonSpy {
 	callsArgOnAsync(index: number, context: any): SinonStub;
 	callsArgWithAsync(index: number, ...args: any[]): SinonStub;
 	callsArgOnWithAsync(index: number, context: any, ...args: any[]): SinonStub;
+	onCall(n: number): SinonStub;
+	onFirstCall(): SinonStub;
+	onSecondCall(): SinonStub;
+	onThirdCall(): SinonStub;
 	yields(...args: any[]): SinonStub;
 	yieldsOn(context: any, ...args: any[]): SinonStub;
 	yieldsTo(property: string, ...args: any[]): SinonStub;