Update opam
Update opam

GeoCoq is not compatible with 8.5 anymore. We also used coq-mathcomp-field library for building a model of the axioms.
gmalecha/opam-coq-archive,gmalecha/opam-coq-archive,gmalecha/opam-coq-archive,mattam82/coq-opam-archive,mattam82/coq-opam-archive,coq/opam-coq-archive,mattam82/coq-opam-archive