fix client_context example from ssl protocol versions docs

Author: graingert

Doc/library/ssl.rst

@@ -2686,8 +2686,8 @@ disabled by default.
 ::
 
    >>> client_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
-   >>> client_context.minimum_version = ssl.TLSVersion.TLSv1_3
-   >>> client_context.maximum_version = ssl.TLSVersion.TLSv1_3
+   >>> client_context.minimum_version = ssl.TLSVersion.TLSv1_2
+   >>> client_context.maximum_version = ssl.TLSVersion.MAXIMUM_VERSION
 
 
 The SSL context created above will only allow TLSv1.2 and later (if