Add missing parameter to docstring

Closes: #4410
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4410
Pull-request-sha: 070a0f44f3

Change-Id: I7a026bf6a2041e7686d90d5f155b88d8001f2ba8
(cherry picked from commit b1e4b59781)

lib/sqlalchemy/util/deprecations.py

@@ -25,6 +25,9 @@ def warn_pending_deprecation(msg, stacklevel=3):
 def deprecated(version, message=None, add_deprecation_to_docstring=True):
     """Decorates a function and issues a deprecation warning on use.
 
+    :param version:
+      Issue version in the warning.
+
     :param message:
       If provided, issue message in the warning.  A sensible default
       is used if not provided.