-Add failure case for old import style

Author: narfman0

flask_restplus/reqparse.py

@@ -4,7 +4,10 @@
 import decimal
 import six
 
-from collections.abc import Hashable
+try:
+    from collections.abc import Hashable
+except ImportError:
+    from collections import Hashable
 from copy import deepcopy
 from flask import current_app, request
 

flask_restplus/swagger.py

@@ -6,7 +6,10 @@
 
 from inspect import isclass, getdoc
 from collections import OrderedDict
-from collections.abc import Hashable
+try:
+    from collections.abc import Hashable
+except ImportError:
+    from collections import Hashable
 from six import string_types, itervalues, iteritems, iterkeys
 
 from flask import current_app