8 hours ago, the job still passed at the top of the the master branch (commit a9bd8925c7fa50dd3cfab125b824ec192133ef49):

https://travis-ci.org/python/cpython/jobs/518281237

"Successfully installed Jinja2-2.10.1 MarkupSafe-1.1.1 Pygments-2.3.1 Sphinx-2.0.1 alabaster-0.7.12 babel-2.6.0 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-2.21.0 six-1.12.0 snowballstemmer-1.2.1 sphinxcontrib-applehelp-1.0.1 sphinxcontrib-devhelp-1.0.1 sphinxcontrib-htmlhelp-1.0.1 sphinxcontrib-jsmath-1.0.1 sphinxcontrib-qthelp-1.0.2 sphinxcontrib-serializinghtml-1.1.3 urllib3-1.24.1"
...
PATH=./venv/bin:$PATH sphinx-build -b doctest -d build/doctrees -D latex_elements.papersize= -q -W -j4 -W . build/doctest 
...
The command "xvfb-run make -C Doc/ PYTHON=../python SPHINXOPTS="-q -W -j4" doctest" exited with 0.

---

6 hours ago, it failed:

https://travis-ci.org/python/cpython/jobs/518572326

Successfully installed Jinja2-2.10.1 MarkupSafe-1.1.1 Pygments-2.3.1 Sphinx-2.0.1 alabaster-0.7.12 babel-2.6.0 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-2.21.0 six-1.12.0 snowballstemmer-1.2.1 sphinxcontrib-applehelp-1.0.1 sphinxcontrib-devhelp-1.0.1 sphinxcontrib-htmlhelp-1.0.1 sphinxcontrib-jsmath-1.0.1 sphinxcontrib-qthelp-1.0.2 sphinxcontrib-serializinghtml-1.1.3 urllib3-1.24.1

Warning, treated as error: (...)

--

In the 2 builds, pip installed the the same Python modules versions.

I compared the raw logs of the 2 builds. In short, they are the same.

Maybe the job already failed previously, but only randomly?