RFR: 8249264: Build validate-headers task fails after JDK-8248261

[alexander . matveev]

Please review the jpackage fix for bug [1] at [2].

Added missing ",".

[1] https://bugs.openjdk.java.net/browse/JDK-8249264
[2] http://cr.openjdk.java.net/~almatvee/8249264/webrev.00/

Thanks,
Alexander