[CI] bump minimum OCaml version

.gitlab-ci.yml

@@ -140,24 +140,6 @@ internal_nightly:
   tags:
    - nix
 
-frama-c-ocaml-4.06:
-  variables:
-    OCAML: "4_06"
-  <<: *frama-c-ocaml
-  only:
-  - schedules
-
-frama-c-ocaml-4.07:
-  variables:
-    OCAML: "4_07"
-  <<: *frama-c-ocaml
-
-frama-c-ocaml-4.05:
-  variables:
-    OCAML: "4_05"
-  <<: *frama-c-ocaml
-
-
 caveat-importer:
   stage: tests
   script:

nix/default.nix

 # paramaterised derivation with dependencies injected (callPackage style)
-{ pkgs, stdenv, src ? ../., opam2nix, ocaml_version ? "ocaml-ng.ocamlPackages_4_05.ocaml", plugins ? { } }:
+{ pkgs, stdenv, src ? ../., opam2nix, ocaml_version ? "ocaml-ng.ocamlPackages_4_08.ocaml", plugins ? { } }:
 
 let mk_buildInputs = { opamPackages ? [], nixPackages ? [] } :
     [ pkgs.gnugrep pkgs.gnused  pkgs.autoconf pkgs.gnumake pkgs.gcc pkgs.ncurses pkgs.time pkgs.python3 pkgs.perl pkgs.file pkgs.which pkgs.dos2unix] ++ nixPackages ++ opam2nix.build {