Use patlib.Path in tests and tools

setup.py

@@ -1,15 +1,13 @@
 # -*- coding: utf-8 -*-
-import io
-import os
+from pathlib import Path
 
 try:
     from setuptools import setup
 except ImportError:
     from distutils.core import setup
 
-this_directory = os.path.dirname(__file__)
-with io.open(os.path.join(this_directory, 'README.md'), encoding='utf-8') as f:
-    long_description = f.read()
+this_directory = Path(__file__).parent
+long_description = this_directory.joinpath('README.md').read_text(encoding='utf-8')
 
 setup(
     name='cibuildwheel',