Incorrect using typeof operator

[Undermuz]

In this code:
https://github.com/postmanlabs/postman-collection/blob/main/lib/collection/response.js#L139
https://github.com/postmanlabs/postman-collection/blob/main/lib/collection/request.js#L63

You are using typeof operator incorrectly, because typeof operator returns string with type name like 'undefined', 'function', etc, but not a type.

[Undermuz]

Fix: #1300