Update last-update date for dry-run

Author: Antoine Pelisse

keps/sig-api-machinery/0015-dry-run.md

@@ -13,7 +13,7 @@ approvers:
   - "@erictune"
 editor: apelisse
 creation-date: 2018-06-21
-last-updated: 2018-06-21
+last-updated: 2020-03-23
 status: implemented
 ---