Replace setup.cfg metadata license_file with license_files

license_file has been deprecated in wheel 0.32.0 in favor of
license_files.

setup.cfg

@@ -25,7 +25,8 @@ classifiers =
 	Programming Language :: Python :: 3.6
 	Programming Language :: Python :: 3.7
 license = MIT
-license_file = LICENSE
+license_files =
+	LICENSE
 description = A pure Python, cross-platform library/tool for reading Macintosh resource data, as stored in resource forks and ``.rsrc`` files
 long_description = file: README.rst
 long_description_content_type = text/x-rst
@@ -40,7 +41,7 @@ keywords =
 
 [options]
 setup_requires =
-	setuptools>=39.2.0
+	setuptools>=42.0.0
 python_requires = >=3.6
 packages = find:
 

tox.ini

@@ -20,7 +20,7 @@ commands = mypy
 [testenv:package]
 deps =
 	twine
-	wheel
+	wheel >= 0.32.0
 
 commands =
 	python setup.py sdist bdist_wheel