MFC r365883: pkgbase: use consistent annotation for object keys

Everywhere else we use objects ("scripts", generally) we do specify the
optional colon. Be consistent and do the same for directories.

PR:		249273

release/packages/runtime.ucl

@@ -30,7 +30,7 @@ deps: {
         version: "%VERSION%"
     }
 }
-directories {
+directories: {
     /dev = "y";
     /tmp = "y";
 }