Fix some small setup.py issues

[njsmith]

As suggested by pyroma

[codecov]

Codecov Report

Merging #202 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #202      +/-   ##
==========================================
- Coverage   99.03%   99.01%   -0.03%     
==========================================
  Files          59       59              
  Lines        7996     7996              
  Branches      568      568              
==========================================
- Hits         7919     7917       -2     
- Misses         61       62       +1     
- Partials       16       17       +1

Impacted Files	Coverage Δ
trio/_util.py	86.07% <0%> (-2.54%)	⬇️

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