Supertest: bump version

Supertest depends on and exposes the interface of superagent.
Therefore, supertest updated its major version to 2.0 when it updated
its superagent dependency to superagent 2.0.

These type definitions also refer to the type definitions for
superagent 2.0, so they apply to supertest 2.0

supertest/index.d.ts

@@ -1,4 +1,4 @@
-// Type definitions for SuperTest v1.1.0
+// Type definitions for SuperTest v2.0.1
 // Project: https://github.com/visionmedia/supertest
 // Definitions by: Alex Varju <https://github.com/varju/>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped