Update Python version specs in setup.cfg

Author: akx

setup.cfg

@@ -11,7 +11,7 @@ packages=['upcloud_api', 'upcloud_api.cloud_manager']
 license = MIT
 
 [options]
-python_requires = >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, !=3.5.*, <4
+python_requires = >=3.6, <4
 setup_requires =
     setuptools
     pytest-runner
@@ -26,8 +26,5 @@ packages =
     upcloud_api
     upcloud_api.cloud_manager
 
-[tox:tox]
-envlist = py27, py36, py37, py38, py39, pypy3
-
 [bdist_wheel]
 universal = 1