My workaround for bpo-31568 is causing new issues on Python 3.5.

Output:
---
0.03s$ pyenv global system 3.5
pyenv: version `3.5' not installed
---

Extract of Python 3.5 .travis.yml:
---
      before_install:
        # work around https://github.com/travis-ci/travis-ci/issues/8363
        - pyenv global system 3.5
---

=> https://github.com/travis-ci/travis-ci/issues/8363

This workaround was added by me:
---
commit 70c630a7316f9f6063557786442e3c56502fe8ea
Author: Victor Stinner <victor.stinner@gmail.com>
Date:   Sun Sep 24 15:45:00 2017 -0700

    bpo-31568, Travis CI: Fix python3.5 (#3737)
    
    Works around Travis CI bug about the python3.5 binary:
    https://github.com/travis-ci/travis-ci/issues/8363
---

Without the workaround, running "python3.5" on Travis CI failed with "pyenv: python3.5: command not found".

Extract of Larry Hastings's email:
---

I have three PRs for Python 3.5.5rc1:

    https://github.com/python/cpython/pull/4656
    https://github.com/python/cpython/pull/5197
    https://github.com/python/cpython/pull/5201

I can't merge them because Travis CI is unhappy.  All three CI tests fail in the same way, reporting this error:

    The command "pyenv global system 3.5" failed and exited with 1 during .
---
https://mail.python.org/pipermail/python-committers/2018-January/005135.html