Allow doc building using earlier versions of Sphinx.
Review Request #10779 — Created Nov. 3, 2019 and discarded — Latest diff uploaded
A recent change required Sphinx 2.1.1+ for doc building, but this version isn't available on Python 2.7. We want to support building using both Python 2.x and 3.x, particularly within CI environments. This change relaxes the version restriction to the latest 1.x release (1.8.5).