obuild is 4.06 ready now

.travis.yml

@@ -105,7 +105,6 @@ install_osx: &install_osx
   - opam init
   - eval `opam config env`
   - opam update
-  - opam pin add obuild --dev-repo --no-action # https://github.com/ocaml-obuild/obuild/pull/167#issuecomment-345937677
   - opam pin add ptmap https://github.com/andyli/ptmap.git#ocaml406 --no-action # https://github.com/backtracking/ptmap/pull/8
   - opam pin add haxe . --no-action
   - opam install haxe --deps-only