Use string types check

[obestwalter]

as suggested here: #617 (review)

[obestwalter]

I have to up my git foo seriously, when juggling different changeset ... sigh

[codecov]

Codecov Report

Merging #627 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #627   +/-   ##
=======================================
  Coverage   93.67%   93.67%           
=======================================
  Files          11       11           
  Lines        2357     2357           
=======================================
  Hits         2208     2208           
  Misses        149      149

Impacted Files	Coverage Δ
tox/_pytestplugin.py	93.97% <100%> (ø)	⬆️

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[obestwalter]

that's better :)

[asottile]

This has different semantics. In python2 string_types is (unicode, bytes) in python3 it is just (str,) -- not sure if that matters in this case but it is the reason that I left it as two separate conditionals.

[obestwalter]

The check only looks if it is some kind of string or a an iterable containing name and version, so that simple test is sufficient.

[asottile]

sweet -- shipit!