With sphinx 2.2, sphinxify throws a deprecation warning:

/usr/share/doc/sage/common/themes/sage/search.html:22: RemovedInSphinx30Warning: To modify script_files in the theme is deprecated. Please insert a <script> tag directly in your theme instead.

Fix taken from rtd_theme [1]

[1] readthedocs/sphinx_rtd_theme@4a7dc08

CC: @kiwifb @timokau @isuruf

Component: documentation

Author: Antonio Rojas

Branch/Commit: e759f94

Reviewer: John Palmieri

Issue created by migration from https://trac.sagemath.org/ticket/29095