Suppress DeprecationWarning from pyramid.path

The warning is not new but for some reason it is now being reported with
the latest pytest release. Possibly related to
pytest-dev/pytest#6681.

tox.ini

@@ -36,6 +36,9 @@ filterwarnings =
     #
     ignore:^Use of \.\. or absolute path in a resource path is not allowed and will raise exceptions in a future release\.$:DeprecationWarning:pkg_resources
 
+    # Fixed in next Pyramid release. See https://github.com/Pylons/pyramid/issues/3553.
+    ignore:the imp module is deprecated in favour of importlib:DeprecationWarning:pyramid.path
+
     # Ignore WebOb warnings that just say "<method> will be changing in the
     # future" and don't say how it will be changing or what developers can do
     # now to avoid the warning. I don't think these warnings _can_ be avoided