Update base url to fix trailing slash redirect

spec/openapi.yaml

@@ -6,7 +6,7 @@ info:
       name: Eclipse Public License - 2.0
       url: https://www.eclipse.org/legal/epl-2.0/
 servers:
-   - url: https://api.eclipse.org/foundation/mailing_lists
+   - url: https://api.eclipse.org/foundation/mailing-list
      description: Production endpoint for the membership portal data
 tags:
    - name: Mailing Lists