Removed redundent assertion(part of it)

Author: thekafkaf

jsonpointer.py

@@ -223,7 +223,7 @@ def walk(self, doc, part):
 
         part = self.get_part(doc, part)
 
-        assert (type(doc) in (dict, list) or hasattr(doc, '__getitem__')), "invalid document type %s" % (type(doc),)
+        assert hasattr(doc, '__getitem__'), "invalid document type %s" % (type(doc),)
 
         if isinstance(doc, Sequence):
             if part == '-':