Restore the ocamlbuild dependency

Previous opam files have been fixed by Fabrice, but the upstream opam was not changed, so this new version was proposed again with broken dependencies. I sent a PR upstream ( ocaml-community/ISO8601.ml#8 ) to make sure it does not happen again.

Author: gasche

packages/ISO8601/ISO8601.0.2.5/opam

@@ -26,4 +26,7 @@ install: [ make "install" ]
 
 remove: [ "ocamlfind" "remove" "ISO8601" ]
 
-depends: [ "ocamlfind" {build} ]
+depends: [
+  "ocamlfind" {build}
+  "ocamlbuild" {build}
+]