ocaml-duff: update to 0.5.

v0.5 2022-04-08 Paris (France)
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* `duff` works only for OCaml >= 4.07 (@hannesm, #11)
* Update with `ocamlformat.0.21.0` (@hannesm, #11)
* Remove the `bigarray-compat` dependency (@hannesm, #11)

v0.4 2021-15-03 Paris (France)
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- Upgrade test to use `hxd.0.3.1`
- Upgrade to `ocamlformat.0.16.0`

v0.3 2020-06-02 Paris (France)
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__breaking changes__

* Add a constraint with `git.2.1.3` (#7)
* Update the documentation (#6)
* Work on the new API (#2)
* Delete provided binary (#5)
* Move to `dune.2.0.0` (#5)
* Integrate fuzzer into tests (#5)
* Apply ocamlformat (#5)

(wiz)