doc: fix links for maven from admin to user

Fix the links from admin docs to user docs for maven repository. User
doc was moved from maven to maven_repository, breaking
all links from admin docs.

doc/administration/maven_repository.md

@@ -7,14 +7,14 @@ in GitLab 11.3. To learn how to use
 When the GitLab Maven Repository is enabled, every project in GitLab will have
 its own space to store [Maven](https://maven.apache.org/) packages.
 
-To learn how to use it, see the [user documentation](../user/project/packages/maven.md).
+To learn how to use it, see the [user documentation](../user/project/packages/maven_repository.md).
 
 ## Enabling the Maven Repository
 
 NOTE: **Note:**
 Once enabled, newly created projects will have the Packages feature enabled by
 default. Existing projects will need to
-[explicitly enabled it](../user/project/packages/maven.md#enabling-the-packages-repository).
+[explicitly enabled it](../user/project/packages/maven_repository.md#enabling-the-packages-repository).
 
 To enable the Maven repository: