docs: fix example jwt expiration epoch

Issue: the example epoch date is wrapped in parentheses. This causes the server to return PGRST303: "The JWT 'exp' claim must be a number"

Fix: remove parentheses
(cherry picked from commit 69d21a82c9)

docs/tutorials/tut1.rst

@@ -172,7 +172,7 @@ Go back to :ref:`tut1_step3` and change the payload to
 
 .. code-block:: bash
 
-  payload=$(echo -n "{\"role\":\"todo_user\",\"exp\":\"123456789\"}" | _base64)
+  payload=$(echo -n "{\"role\":\"todo_user\",\"exp\":123456789}" | _base64)
 
   echo -n "$header.$payload.$signature"