Homepage URL on opam listing for easy-format is a 404

[johnwhitington]

OPAM page: https://opam.ocaml.org/packages/easy-format/easy-format.1.3.1/

Link in question: http://mjambon.com/easy-format.html (redirects to the https version, but still 404)

[mjambon]

The opam package at opam-repository needs to be made to point to https://mjambon.github.io/mjambon2016/easy-format.html
It hasn't been updated in a while but it should be better than a 404.

PR: ocaml/opam-repository#25223