Update stale.yml

Author: songyumeng

.github/stale.yml

@@ -7,6 +7,7 @@ exemptLabels:
   - help wanted
   - bug
   - enhancement
+  - feature
 # Label to use when marking an issue as stale
 staleLabel: stale
 # Comment to post when marking an issue as stale. Set to `false` to disable