gistfile1.txt

$ opam upgrade -v
Everything as up-to-date as possible.
The following newer versions couldn't be installed:
  - base-bytes.legacy is not available because it requires OCaml < 4.02.0.
  - camlp4.4.03.0 is not available because it requires OCaml >= 4.03.0.
The following would require downgrades or uninstalls, but you may upgrade them explicitely:
  - async.112.24.00
  - async_extra.112.24.00
  - async_kernel.112.24.00
  - async_unix.112.24.00
  - bignum.112.24.00
  - bin_prot.112.24.00
  - core.112.24.00
  - core_kernel.112.24.00
  - custom_printf.112.24.00
  - pa_ounit.112.24.00
  - pa_test.112.24.00
  - sexplib.112.24.00
  - tls.0.4.0
  - typerep.112.24.00
  - websocket.0.9.3
  - x509.0.3.0