setup: Update trove classifiers.

Author: htgoebel

setup.py

@@ -74,9 +74,8 @@ def read(filename):
 Operating System :: POSIX :: SunOS/Solaris
 Programming Language :: C
 Programming Language :: Python
-Programming Language :: Python :: 2
-Programming Language :: Python :: 2.7
 Programming Language :: Python :: 3
+Programming Language :: Python :: 3 :: Only
 Programming Language :: Python :: 3.5
 Programming Language :: Python :: 3.6
 Programming Language :: Python :: 3.7