Fix the lower TypeScript version

should-sinon depends on sinon but has a lower required TypeScript version.

types/should-sinon/index.d.ts

@@ -2,7 +2,7 @@
 // Project: https://github.com/shouldjs/sinon
 // Definitions by: AryloYeung <https://github.com/Arylo>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
-// TypeScript Version: 2.1
+// TypeScript Version: 2.3
 
 import * as s from "sinon";
 import should = require("should");