Rely on Python syntax for pwd keyword argument.

zipp.py

@@ -209,13 +209,12 @@ def __init__(self, root, at=""):
         self.root = FastLookup.make(root)
         self.at = at
 
-    def open(self, mode='r', *args, **kwargs):
+    def open(self, mode='r', *args, pwd=None, **kwargs):
         """
         Open this entry as text or binary following the semantics
         of ``pathlib.Path.open()`` by passing arguments through
         to io.TextIOWrapper().
         """
-        pwd = kwargs.pop('pwd', None)
         zip_mode = mode[0]
         stream = self.root.open(self.at, zip_mode, pwd=pwd)
         if 'b' in mode: