Travis CI: "Documentation tests" failed with:

Successfully installed Jinja2-2.10.1 MarkupSafe-1.1.1 Pygments-2.4.2 Sphinx-2.1.0 alabaster-0.7.12 babel-2.7.0 blurb-1.0.7 certifi-2019.3.9 chardet-3.0.4 docutils-0.14 idna-2.8 imagesize-1.1.0 packaging-19.0 pyparsing-2.4.0 python-docs-theme-2018.7 pytz-2019.1 requests-2.22.0 six-1.12.0 snowballstemmer-1.2.1 sphinxcontrib-applehelp-1.0.1 sphinxcontrib-devhelp-1.0.1 sphinxcontrib-htmlhelp-1.0.2 sphinxcontrib-jsmath-1.0.1 sphinxcontrib-qthelp-1.0.2 sphinxcontrib-serializinghtml-1.1.3 urllib3-1.25.3
(...)
Warning, treated as error:
duplicate object description of email.message, other instance in library/email.message, use :noindex: for one of them

https://travis-ci.org/python/cpython/jobs/540532864

ref: https://github.com/python/cpython/pull/13762

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Sphinx 2.1 was released yesterday:

https://www.sphinx-doc.org/en/master/changes.html#release-2-1-0-released-jun-02-2019