File name needs version

Without it it's not loaded correctly, i.e. "Gerrit print Loaded plugin
stale-packed, version refs" while starting up

Change-Id: I92668d48905486279e014e82935ea0b5c178768f
diff --git a/admin/stale-packed-refs.groovy b/admin/stale-packed-refs-1.0.groovy
similarity index 100%
rename from admin/stale-packed-refs.groovy
rename to admin/stale-packed-refs-1.0.groovy