Fix deprecated use of collections module

In Python 3.8 imports of abstract base classes directly from the `collections` module will stop working entirely. This change maintains existing behaviour whilst providing backwards compatibility.

Author: amrishparmar

nameparser/config/__init__.py

@@ -29,8 +29,13 @@
 unexpected results. See `Customizing the Parser <customize.html>`_.
 """
 from __future__ import unicode_literals
-import collections
+
 import sys
+try:
+    # Python 3.3+
+    from collections.abc import Set
+except ImportError:
+    from collections import Set
 
 from nameparser.util import binary_type
 from nameparser.util import lc
@@ -45,10 +50,10 @@
 
 DEFAULT_ENCODING = 'UTF-8'
 
-class SetManager(collections.Set):
+class SetManager(Set):
     '''
     Easily add and remove config variables per module or instance. Subclass of
-    ``collections.Set``.
+    ``collections.abc.Set``.
     
     Only special functionality beyond that provided by set() is
     to normalize constants for comparison (lower case, no periods)