Fix runner api doc

doc/api/runners.md

@@ -159,7 +159,7 @@ PUT /runners/:id
 | `tag_list`    | array   | no       | The list of tags for a runner; put array of tags, that should be finally assigned to a runner |
 | `run_untagged`    | boolean   | no       | Flag indicating the runner can execute untagged jobs |
 | `locked`    | boolean   | no       | Flag indicating the runner is locked |
-| `access_level`    | integer   | no       | The access_level of the runner; `not_protected` or `ref_protected` |
+| `access_level`    | string   | no       | The access_level of the runner; `not_protected` or `ref_protected` |
 
 ```
 curl --request PUT --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" "https://gitlab.example.com/api/v4/runners/6" --form "description=test-1-20150125-test" --form "tag_list=ruby,mysql,tag1,tag2"