Fix wrong example url (`repositories` instead of `repository`)

doc/api/repository_submodules.md

@@ -22,7 +22,7 @@ PUT /projects/:id/repository/submodules/:submodule
 | `commit_message` | string | no | Commit message. If no message is provided, a default one will be set |
 
 ```sh
-curl --request PUT --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" "https://gitlab.example.com/api/v4/projects/5/repositories/submodules/lib%2Fmodules%2Fexample"
+curl --request PUT --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" "https://gitlab.example.com/api/v4/projects/5/repository/submodules/lib%2Fmodules%2Fexample"
 --data "branch=master&commit_sha=3ddec28ea23acc5caa5d8331a6ecb2a65fc03e88&commit_message=Update submodule reference"
 ```