Upgrade opam file to 2.0

Signed-off-by: Jeremie Dimino <[email protected]>

Author: jeremiedimino

ppx_expect.opam

@@ -1,4 +1,4 @@
-opam-version: "1.2"
+opam-version: "2.0"
 version: "v0.11.1"
 maintainer: "[email protected]"
 authors: ["Jane Street Group, LLC <[email protected]>"]
@@ -24,8 +24,8 @@ depends: [
   "ocaml-migrate-parsetree" {>= "1.0"}
   "ppxlib"                  {>= "0.1.0"}
   "re"                      {>= "1.5.0"}
+  "ocaml"                   {>= "4.04.1"}
 ]
-available: [ ocaml-version >= "4.04.1" ]
 descr: "
 Cram like framework for OCaml