(DOCSP-36948) Changes authorization to authentication in one spot (#163)

Author: sarahsimpers

source/fundamentals/authentication.txt

@@ -145,7 +145,7 @@ string as follow:
 
 .. tip:: Default Mechanism
 
-   MongoDB version 4.0 uses ``SCRAM-SHA-1`` as the default authorization mechanism
+   MongoDB version 4.0 uses ``SCRAM-SHA-1`` as the default authentication mechanism
    if the server does not support ``SCRAM-SHA-256``.
 
    To learn more on specifying the default mechanism, see :ref:`csharp-authentication-default`.