Use "stale" label for stale bot (#1200)

"wontfix" seems to imply more than "no activity", when we actually are
okay with reopening previously closed issues with no resolution

Signed-off-by: Wilson E. Husin <whusin@vmware.com>

.github/stale.yml

@@ -8,7 +8,7 @@ exemptLabels:
  - security
  - wip
 # Label to use when marking an issue as stale
-staleLabel: wontfix
+staleLabel: stale
 # Comment to post when marking an issue as stale. Set to `false` to disable
 markComment: >
  There has not been much activity here.