Add version constraint to the docutils dependency

[peterzahemszky]

Add a version constraint to the docutils dependency to resolve problems with Sphinx.

Closes #574.

[codecov-commenter]

Codecov Report

Merging #575 (d82b2f5) into master (fc5f0ae) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #575   +/-   ##
=======================================
  Coverage   95.35%   95.35%           
=======================================
  Files          92       92           
  Lines        4305     4305           
  Branches      277      277           
=======================================
  Hits         4105     4105           
  Misses        140      140           
  Partials       60       60           

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[flongford]

Thanks for spotting this @peterzahemszky - in order to catch any further regressions, could we include running make docs as part of our CI builds?

I think we only need to do so on one of the target OS (i.e. Ubuntu).

Scratch that - we already do it:

simphony-remote/.github/workflows/build_test_ubuntu18.yml

Lines 48 to 51 in fc5f0ae

	- name: Build docs
	run: |
	. venv/bin/activate
	make docs

[flongford]

LGTM!