Replace deprecated utcfromtimestamp

Author: hugovk

Doc/library/ssl.rst

@@ -388,8 +388,8 @@ Certificate handling
       >>> timestamp = ssl.cert_time_to_seconds("Jan  5 09:34:43 2018 GMT")
       >>> timestamp  # doctest: +SKIP
       1515144883
-      >>> print(dt.datetime.utcfromtimestamp(timestamp))  # doctest: +SKIP
-      2018-01-05 09:34:43
+      >>> print(dt.datetime.fromtimestamp(timestamp, dt.UTC))  # doctest: +SKIP
+      2018-01-05 09:34:43+00:00
 
    "notBefore" or "notAfter" dates must use GMT (:rfc:`5280`).