Single line praefect repository migration command

During a Gitaly demo, we noticed copy pasting the curl command in to
shell and replacing the private token was more difficult than necessary
due to the command being multiline. This commit single lines the
multiline curl command.

doc/administration/gitaly/praefect.md

@@ -703,10 +703,7 @@ Repositories may be moved from one storage location using the [Repository
 API](../../api/projects.html#edit-project):
 
 ```shell
-curl --request PUT \
-  --header "PRIVATE-TOKEN: <your_access_token>" \
-  --data "repository_storage=praefect" \
-  https://example.gitlab.com/api/v4/projects/123
+curl --request PUT --header "PRIVATE-TOKEN: <your_access_token>" --data "repository_storage=praefect" https://example.gitlab.com/api/v4/projects/123
 ```
 
 ## Debugging Praefect