tox: Update pylint/astroid to 1.5.4/1.4.4.

pylint:

* Merge StringMethodChecker with StringFormatChecker. This fixes a
  bug where disabling all the messages and enabling only a handful of
  messages from the StringFormatChecker would have resulted in no
  messages at all.

* Don't apply unneeded-not over sets.

astroid:

* unpack_infer raises InferenceError if it can't operate
  with the given sequences of nodes.

* Support accessing properties with super().

* Enforce strong updates per frames.

  When looking up a name in a scope, Scope.lookup will return
  only the values which will be reachable after execution, as seen
  in the following code:

       a = 1
       a = 2

  In this case it doesn't make sense to return two values, but
  only the last one.

tox.ini

@@ -106,8 +106,8 @@ passenv =
 deps =
     {[testenv]deps}
     {[testenv:misc]deps}
-    astroid==1.4.3
-    pylint==1.5.3
+    astroid==1.4.4
+    pylint==1.5.4
     requests==2.9.1
 commands =
     {envpython} scripts/link_pyqt.py --tox {envdir}