Fix METADATA format for tools/external_updater

Change-Id: Id95f7cc59d27b4dc740073273e5908c9cd2728a0

METADATA

diff --git a/METADATA b/METADATA
index 57b9db4..3e1e6b5 100644
--- a/METADATA
+++ b/METADATA
@@ -9,6 +9,6 @@
     value: "https://github.com/google/subcommands.git"
   }
   version: "v1.2.0"
-  last_upgrade_date { year: 2019 month: 09 day: 05 }
+  last_upgrade_date { year: 2019 month: 9 day: 5 }
   license_type: NOTICE
 }