Poetry: Lock pathlib2 to make pytest happy

For some reason, the latest pytest version doesn't want pathlib2 at 2.3.5

[SolverProblemError]
Because no versions of pytest match <4.6.11 || >4.6.11,<4.7.0
 and pytest (4.6.11) depends on pathlib2 (>=2.2.0), pytest (<4.7.0) requires pathlib2 (>=2.2.0).
And because no versions of pathlib2 match >=2.2.0,<2.3.5 || >2.3.5
 and pathlib2 (2.3.5) depends on scandir (*), pytest (<4.7.0) requires scandir (*).
So, because no versions of scandir match *
 and tmuxp depends on pytest (<4.7.0), version solving failed.

Author: tony

poetry.lock

@@ -30,6 +30,7 @@ pytest = [
   {version="<4.7.0", python="<3"},
   {version="*", python=">=3"}
 ]
+pathlib2 = {version="<2.3.5", python="<3"}  # Untangle pytest peer-dependency
 pytest-rerunfailures = "*"
 sphinx = [
   {version="<2", python="<3"},