Fix class reference

[Gallaecio]

This class reference was broken.

It was detected in Parsel, which inherits this documentation through InterSphinx.

[wRAR]

pkg_resources.VersionConflict: (pytest 4.1.0 (/home/travis/virtualenv/python3.5.6/lib/python3.5/site-packages), Requirement.parse('pytest>=4.6'))

[Gallaecio]

I see no pytest version requirement. I’m retrying the build, see if it is reproducible.

[wRAR]

Previously only the 3.5 test failed, now all of them did.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@eb40f21). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #110   +/-   ##
=========================================
  Coverage          ?   95.52%           
=========================================
  Files             ?        3           
  Lines             ?      759           
  Branches          ?      128           
=========================================
  Hits              ?      725           
  Misses            ?       19           
  Partials          ?       15           

Impacted Files	Coverage Δ
cssselect/xpath.py	94.89% <ø> (ø)

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[Gallaecio]

So, if we do not force it, the system pytest version is used, but it seems the version of some dependency is installed (pytest-cov?) that is incompatible with the system pytest version. I’m not 100% sure, though.

[wRAR]

Please merge if you think it's fine.