Allow coverage 5.x

[felixonmars]

All tests pass here with coverage 5.2.

[codecov]

Codecov Report

Merging #340 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #340   +/-   ##
=======================================
  Coverage   95.94%   95.94%           
=======================================
  Files           3        3           
  Lines        1184     1184           
=======================================
  Hits         1136     1136           
  Misses         48       48           

Impacted Files	Coverage Δ
setup.py	0.00% <ø> (ø)

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[markstory]

Thank you 👍