add missing kwargs, accidentally (?) removed in 13aa4d0 (required for backwards compatibility)

Author: jschlyter

src/cryptojwt/jwk.py

@@ -396,7 +396,7 @@ def serialize(self, private=False):
         """
         pass
 
-    def get_key(self, private=False):
+    def get_key(self, private=False, **kwargs):
         """
         Get a keys useful for signing and/or encrypting information.