Fix project id param for merge request version API

doc/api/merge_requests.md

@@ -905,7 +905,7 @@ GET /projects/:id/merge_requests/:merge_request_id/versions
 
 | Attribute | Type    | Required | Description           |
 | --------- | ------- | -------- | --------------------- |
-| `id`      | integer | yes      | The ID of the project |
+| `id`      | String  | yes      | The ID of the project |
 | `merge_request_id` | integer | yes | The ID of the merge request |
 
 ```bash

lib/api/merge_request_diffs.rb

@@ -10,8 +10,8 @@ module API
       end
 
       params do
-        requires :id, type: Integer, desc: 'The ID of a project'
-        requests :merge_request_id, type: Integer, desc: 'The ID of a merge request'
+        requires :id, type: String, desc: 'The ID of a project'
+        requires :merge_request_id, type: Integer, desc: 'The ID of a merge request'
       end
 
       get ":id/merge_requests/:merge_request_id/versions" do