require sphinx 2.2.2 explicitly so docs build

[murdomoyse]

• Please check if the Pull Request fulfills these requirements

• [ x] The commit message is clear and concise
• [x ] Test for the changes have been added and reviewed
• [x ] Documentation has been added to all new features and edited code has had documentation reviewed

• What kind of change does this Pull request introduce? (Bug fix, feature, docs update, ...)

• What is the current behaviour? (Link to a current open issue if possible)

• What is the new behaviour? (is this a feature change?)

• Does this Pull Request introduce a breaking change? (What changes might users need to make in their application due to this PR?) No

[codecov]

Codecov Report

Merging #130 (29adedf) into master (03af947) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #130   +/-   ##
=======================================
  Coverage   94.72%   94.72%           
=======================================
  Files          44       44           
  Lines        1480     1480           
=======================================
  Hits         1402     1402           
  Misses         78       78           

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[georgeRobertson]

Good stuff