Remove SingleDispatchABC from py3.6 onwards

Author: Tim Mitchell

methoddispatch/methoddispatch36.py

@@ -6,7 +6,7 @@
 from weakref import WeakKeyDictionary
 import warnings
 
-__all__ = ['singledispatch', 'register', 'SingleDispatch', 'SingleDispatchABC']
+__all__ = ['singledispatch', 'register', 'SingleDispatch']
 
 
 ################################################################################

test.py

@@ -2,7 +2,12 @@
 import unittest
 
 import methoddispatch
-from methoddispatch import singledispatch, SingleDispatch, SingleDispatchABC
+from methoddispatch import singledispatch, SingleDispatch
+try:
+    from methoddispatch import SingleDispatchABC
+except ImportError:
+    SingleDispatchABC = SingleDispatch
+
 import abc
 import doctest
 import six