Sphinx build breaks, possibly due to recent version change

[pjbreaux]

The travis build for docs in this repo breaks due to the following error:

Exception occurred:

  File "/home/travis/virtualenv/python2.7.13/lib/python2.7/site-packages/sphinx/themes/classic/../basic/layout.html", line 108, in template

    {%- for css in css_files %}

TypeError: 'NoneType' object is not iterable

The full traceback has been saved in /tmp/sphinx-err-_fpLfF.log, if you want to report the issue to the developers.

Please also report this if it was a user error, so that a better error message can be provided next time.

A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!

make: *** [html] Error 1

The command "make html" exited with 2.

0.00s$ cd ../

[jputrino]

This issue was resolved by upgrading to a newer version of sphinx.