fixed issue

Author: ajburnle

articles/active-directory/fundamentals/toc.yml

@@ -38,7 +38,7 @@
     - name: Group-based licensing
       href: active-directory-licensing-whatis-azure-portal.md
     - name: Default user permissions
-      href: users-default-permissions.m
+      href: users-default-permissions.md
   - name: Architecture
     items:
   - name: Azure AD architecture