Update stale.yml

Signed-off-by: Julius Härtl <jus@bitgrid.net>

.github/stale.yml

@@ -5,6 +5,7 @@ daysUntilClose: 7
 # Issues with these labels will never be considered stale
 exemptLabels:
   - enhancement
+  - bug
 # Label to use when marking an issue as stale
 staleLabel: wontfix
 # Comment to post when marking an issue as stale. Set to `false` to disable