Log Message:
security/ocaml-safepass: Update to 3.1

Upstream does not publish NEWS, but it appears changes are:
  - bugfixes (listed as "remove warnings" :-)
  - change from jbuilder to dune

Changing to dune -- which 3.0 is documented to use but apparently does
not -- makes the package, which is configured to use dune, build.
(Calling this an improvement without further understanding.)