Fix broken Python 2 build (#453)

f2c1298 accidentally broke the build as collections.abc is only available in Python 3.x.

This commit adds a workaround that enables the import that works both on 2 and 3.

Author: bessbd

src/cloudant/_common_util.py

@@ -19,12 +19,16 @@
 
 import sys
 import platform
-from collections.abc import Sequence
 import json
 
 from ._2to3 import LONGTYPE, STRTYPE, NONETYPE, UNITYPE, iteritems_
 from .error import CloudantArgumentError, CloudantException, CloudantClientException
 
+try:
+    from collections.abc import Sequence
+except ImportError:
+    from collections import Sequence
+
 # Library Constants
 
 USER_AGENT = '/'.join([