RFR:8163793: jlink has typo in copy-files plugin help text example

[Srinivas Dama]

Hi,

This patch fixes very small typo error.

Please review http://cr.openjdk.java.net/~sdama/8163793/webrev.00/ for
https://bugs.openjdk.java.net/browse/JDK-8163793 


Regards,
Srinivas