Merge pull request #1972 from jdufresne/py3-only

Add 'Programming Language :: Python :: 3 :: Only' trove classifier

Author: jaraco

setup.cfg

@@ -36,6 +36,7 @@ classifiers =
     License :: OSI Approved :: MIT License
     Operating System :: OS Independent
     Programming Language :: Python :: 3
+    Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7