fix project requirements (some dependencies not py39 compatible)

Author: mueslo

setup.cfg

@@ -1,5 +1,2 @@
 [metadata]
 description-file = README.md
-
-[tool:pytest]
-accept-encodings=utf-8

setup.py

@@ -45,9 +45,11 @@ def find_version(*file_paths):
         "musicbrainzngs~=0.7",
         "terminaltables~=3.1",
     ],
-    python_requires=">=3.5,<4.0",
+    python_requires=">=3.5,<3.9",
     tests_require=['tox', 'pytest', 'flake8', 'pytest-logbook'],
     classifiers=[
+        "Development Status :: 5 - Production/Stable",
+        "Environment :: Console",
         "Operating System :: OS Independent",
         "Programming Language :: Python",
         "Programming Language :: Python :: 3",