pkgbase: use consistent annotation for objectk eys

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

PR:		249273
Submitted by:	Martin <martin.jakob gmx com>
MFC after:	1 week

release/packages/runtime.ucl

@@ -23,7 +23,7 @@ scripts: {
 	chmod 1777 ${PKG_ROOTDIR}/tmp
 EOD
 }
-directories {
+directories: {
     /dev = "y";
     /tmp = "y";
 }