update docs to use port 18381 for the discovery API endpoint

The port is 18381, not 8003.  In fact, 8003 is even bound by devstack which
claims it to be "LMS for Bok Choy".

docs/getting_started.rst

@@ -48,8 +48,8 @@ A new OAuth 2.0 client can be created at ``http://127.0.0.1:8000/admin/oauth2/cl
     1. Click the :guilabel:`Add client` button.
     2. Leave the user field blank.
     3. Specify the name of this service, ``Course Discovery Service``, as the client name.
-    4. Set the :guilabel:`URL` to the root path of this service: ``http://localhost:8003/``.
-    5. Set the :guilabel:`Redirect URL` to the OIDC client endpoint: ``http://localhost:8003/complete/edx-oidc/``.
+    4. Set the :guilabel:`URL` to the root path of this service: ``http://localhost:18381/``.
+    5. Set the :guilabel:`Redirect URL` to the OIDC client endpoint: ``http://localhost:18381/complete/edx-oidc/``.
     6. Copy the :guilabel:`Client ID` and :guilabel:`Client Secret` values. They will be used later.
     7. Select :guilabel:`Confidential (Web applications)` as the client type.
     8. Click :guilabel:`Save`.