Update stale-bot config.

.github/stale.yml

+# Number of days of inactivity before an Issue or Pull Request becomes stale
+daysUntilStale: 60
+
+# Number of days of inactivity before an Issue or Pull Request with the stale label is closed.
+# Set to false to disable. If disabled, issues still need to be closed manually, but will remain marked as stale.
+daysUntilClose: 7
+
+issues:
+  exemptLabels:
+    - acknowledged
+
+# Comment to post when marking as stale. Set to `false` to disable
+markComment: >
+  This issue has been automatically marked as stale because it has not had
+  recent activity. It will be closed if no further activity occurs. Thank you
+  for your contributions.
+
+# Comment to post when closing a stale Issue or Pull Request.
+closeComment: >
+  This issue has been closed due to inactivity.
+
+# Limit the number of actions per hour, from 1-30. Default is 30
+limitPerRun: 1