Fix DeprecationWarning about collections.abc

Fixes #51

CHANGES.rst

@@ -2,14 +2,15 @@
 CHANGES
 =======
 
-5.4 (unreleased)
-----------------
+5.3.1 (unreleased)
+------------------
 
-- Nothing changed yet.
+- Fix a ``DeprecationWarning`` on Python 3. See `issue 51
+  <https://github.com/zopefoundation/zope.testbrowser/issues/51>`_.
 
 
-5.3 (2018-10-10)
-----------------
+5.3.0 (2018-10-10)
+------------------
 
 - Add support for Python 3.7.
 

setup.py

@@ -27,7 +27,7 @@
 
 setup(
     name='zope.testbrowser',
-    version='5.4.dev0',
+    version='5.3.1.dev0',
     url='https://github.com/zopefoundation/zope.testbrowser',
     license='ZPL 2.1',
     description='Programmable browser for functional black-box tests',

src/zope/testbrowser/_compat.py

@@ -29,18 +29,18 @@
     import urllib2 as urllib_request
     from cgi import escape as html_escape
     from urllib import urlencode
-    from UserDict import DictMixin
     from base64 import encodestring as base64_encodebytes
-
-    class MutableMapping(object, DictMixin):
-        pass
 else:
     import http.cookies as httpcookies  # noqa
     import urllib.parse as urlparse  # noqa
     from urllib.parse import quote as url_quote  # noqa
     import urllib.request as urllib_request  # noqa
     from urllib.parse import urlencode  # noqa
     import http.client as httpclient  # noqa
-    from collections import MutableMapping  # noqa
     from html import escape as html_escape  # noqa
     from base64 import encodebytes as base64_encodebytes  # noqa
+
+try:
+    from collections.abc import MutableMapping
+except ImportError:
+    from collections import MutableMapping