use shutil.copytree isntead of outdated distutils.dir_util

[solarw]

Proposed changes

use shutil.copytree isntead of outdated distutils.dir_util

Fixes

#553

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

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If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

DELETE INCLUSIVE THIS AND BELOW FOR STANDARD PR

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Version number: [e.g. 1.0.1]

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[solarw]

@DavidMinarsch @angrybayblade
to be compatible with all the tests shutil.copytree requires dirs_exist_ok=True option, introduced in python 3.8.

so it's not compatible with python3.7 and this PR is meaningless.