Use MOI.AllDifferent

[blegat]

The code was written before MOI had its version of AllDifferent. It should now use MOI.AllDifferent so that the same model that can be solved by MiniZinc.jl etc... can also be solved by this package

[coveralls]

Pull Request Test Coverage Report for Build 11256032217

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 14 of 14 (100.0%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.1%) to 95.383%

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Totals
Change from base Build 10449145917:	-0.1%
Covered Lines:	5020
Relevant Lines:	5263

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💛 - Coveralls

[dourouc05]

The PR looks good!