Yes, in this case I would put something like this on top of the file:

    # Fork by TekMol of https://github.com/feross/is-buffer
    # Which is MIT licensed by Feross Aboukhadijeh

I am actually never completely sure how to properly do this. Would the next forker write the following then?

    # Fork by Joe of https://github.com/tekmol/isBuffer
    # Which is a fork by TekMol of https://github.com/feross/is-buffer
    # Which is MIT licensed by Feross Aboukhadijeh

Looking at that function, I'm not convinced that it's copyrightable in the first place. Once you know what it's supposed to do, how else would you express it?

Of course it's only appropriate to credit the author anyway, and one way to do that nicely is by following the license requirements. I just think "violation of the license" is a bit of an unnecessarily strong statement, given the triviality and the likely non-copyrightability of the code.

Your lawyer's opinion may vary.