update to OTS v8.1.1

[gagath]

OTS has been updated to v8.1.1 recently: https://github.com/khaledhosny/ots/commit/d6d783c67b4aa604edd12dce0decc18a5c79906b

This PR updates the setup.cfg to reflect this change.

After this PR is merged, a new release tag has to be created by the maintainer in order to be able to download the v8.1.1 release tar directly from Github.

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[anthrotype]

Updated to 8.1.2 in master