Update stale.yml

Author: matthew-dean

.github/stale.yml

@@ -4,8 +4,8 @@ daysUntilStale: 120
 daysUntilClose: 14
 # Issues with these labels will never be considered stale
 exemptLabels:
-  - Up-For-Grabs
-  - Bug
+  - up-for-grabs
+  - bug
 # 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