rfcs/draft-gilmore-taht-v4uniext.txt fix

[gregbo]

I'm not sure why the links for [IEN48], [IETF-13], and [IHML] weren't generated in the References section, but here's what they would look like if they had been:

[IEN48] Cerf, V., "The CATENET MODEL FOR INTERNETWORKING", 1978,
https://www.rfc-editor.org/ien/ien48.txt

[IETF-13] Gross, P., Bowers, K., "IETF Proceedings", 1989,
https://www.ietf.org/proceedings/13.pdf

[IHML] Many, T., "Internet History Mailing list", 2019,
http://www.postel.org/internet-history/

[dtaht]

Thank you! despite trying a couple times the tool we are using did not want to do this. I'd love it if you could attempt building the text from the markdown and telling me what to do!!! (how is described in the readme)