Update pyproject.toml license declaration

pyproject.toml

@@ -13,12 +13,13 @@ dependencies = [
     "requests >= 2.25.1",  # Wiki API requests
     "requests_oauthlib >= 1.3.0",  # API authentication via OAuth
 ]
+license = "MIT"
+license-files = ["LICENSE"]
 keywords = ["earwig", "earwigbot", "irc", "wikipedia", "wiki", "mediawiki"]
 classifiers = [
     "Development Status :: 3 - Alpha",
     "Environment :: Console",
     "Intended Audience :: Developers",
-    "License :: OSI Approved :: MIT License",
     "Natural Language :: English",
     "Operating System :: OS Independent",
     "Programming Language :: Python :: 3",