Linux package creation licence warning

[AdamCarroll]

Building the .deb file on Linux results in a warning about a missing licence:

$ ./gradlew jfxNative
Starting a Gradle Daemon (subsequent builds will be faster)

> Task :package:jfxNative 
Debian packages should specify a license.  The absence of a license will cause some linux distributions to complain about the quality of the application.
This bundler might take some while longer than expected.
For details about this, please go to: https://wiki.debian.org/Teams/Dpkg/FAQ#Q:_Why_is_dpkg_so_slow_when_using_new_filesystems_such_as_btrfs_or_ext4.3F

VocabHunter is Open Source software under the Apache 2.0. licence and so it should be possible to include the licence file and avoid this problem.