Better description of statuscode handling and improve example

[DanielRuf]

Currently https://nodejs.org/api/http.html#http_http_get_url_options_callback mentions only 200 but any 2xx statuscode is a success and not an error.

This should be improved.

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[szhigunov]

Hi, I can handle that.

[Trott]

@DanielRuf What do you think the code should check for instead? A previous contributor's attempt to make the status code check more lenient resulted in this comment:

I think the original is better. If that endpoint is expected to return 200 it is better to be strict. Also 201 is not usually used for a GET request, 204 has no content, etc.