docs(ngMock/angular-mocks) added response to whenPOST mock

Request Type: docs

How to reproduce:

Component(s): ngMocks

Impact: small

Complexity: small

This issue is related to: whenPOST

Detailed Description:

The  ```whenPOST``` method should return a response containing status, response body and headers. If omitted the following error will be thrown:

```Uncaught TypeError: Cannot read property '2' of undefined```

The documentation doesn't make it very clear, so I think it will be appropriate to add.

Other Comments: