Fix stalebot exempt labels

.github/stale.yml

@@ -9,7 +9,7 @@ daysUntilClose: 15
 
 # Issues or Pull Requests with these labels will never be considered stale. Set to `[]` to disable
 exemptLabels:
-  - on-hold
+  - on hold
 
 # Set to true to ignore issues in a project (defaults to false)
 exemptProjects: false