Change arcconfig to point to the Phabricator callsign pointing to htt…

…ps://github.com/yugabyte/yugabyte-db

Summary: Change arcconfig to point to the Phabricator callsign pointing to https://github.com/yugabyte/yugabyte-db.

Test Plan:
Submitting this diff using "arc diff".
Jenkins: skip

Reviewers: arnav, wesley, mikhail

Reviewed By: mikhail

Subscribers: ybase

Differential Revision: https://phabricator.dev.yugabyte.com/D6904

.arcconfig

@@ -1,6 +1,6 @@
 {
   "phabricator.uri" : "https://phabricator.dev.yugabyte.com/",
-  "repository.callsign": "YB",
+  "repository.callsign": "YBDB",
   "git:arc.feature.start.default" : "origin/master",
   "arc.land.onto.default": "master",
   "arc.land.remote.default": "origin",