Fixes coq-8.3: requires OCaml 3.12 and lablgtk 2.14

The distinction between `pkgs.ocamlPackages_3_10_0` and `ocamlPackages_3_10_0` makes my head hurt.  There could be a difference when package overrides are used.  Rather than think about it, I'll let it go and worry about it when it becomes a problem.