[fetch] null body status '101' needs to be considered as a distinct code (#94)

>From the issue: https://github.com/whatwg/fetch/issues/86, we can see that null body status is added in link: https://fetch.spec.whatwg.org/#statuses. But for status code 101, it will throw range error, as it is covered in step1 ( status range 200 to 599 ), so for status 101 it will be covered under Range error. 
since the null body status list is used elsewhere too and there 101 needs to
be considered as a distinct code. so we need to make a clear note on these.

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https://github.com/whatwg/fetch/issues/94