Release Metafacture core 6.1.2

[dr0i]

This release fixes a bug introduced in 6.1.1 https://github.com/metafacture/metafacture-core/issues/546.

All new features since 6.0.0 will be documented in 6.1.2.

• [x] update dependencies if these are promising to not break much
• [x] (as this is a quick-bug fix release only affecting MARC-XML producing programs there is no real test release candidate. Playground and oersi test were successfully done.)
• [x] release on maven central
• [x] release on github
• [x] release metafacture-fix 1.1.2
• [x] release metafacture-playground 1.1.2
• [x] update flux-commands
• [x] copy metafacture-fix' functions-and-cookbook to https://github.com/metafacture/metafacture-documentation/blob/master/docs/fix/Fix-functions-and-Cookbook.md
• [x] write blog post, see PR
• [x] toot
• [x] write to email list
• [x] announce at metadaten.community

[dr0i]

All done here. Closing.