chore: remove pathlib dependency

[IceTDrinker]

• the project targets python 3.6+ which have pathlib by default
• the pathlib dependency in pyproject.toml is deprecated
• it caused issues in poetry environment installation of nbmake

Signed-off-by: IceTDrinker 49040125+IceTDrinker@users.noreply.github.com

[gitpod-io[bot]]

[codecov[bot]]

Codecov Report

Merging #48 (eb8f151) into main (3ad0a35) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #48   +/-   ##
=======================================
  Coverage   91.36%   91.36%           
=======================================
  Files           4        4           
  Lines         139      139           
=======================================
  Hits          127      127           
  Misses         12       12           

Impacted Files	Coverage Δ
src/nbmake/pytest_items.py	88.46% <100.00%> (ø)

[alex-treebeard]

Thanks @IceTDrinker. Just released this in version 0.9

[IceTDrinker]

Thanks @IceTDrinker. Just released this in version 0.9

Thank you very much !