jfreereport_libloader: [deprecation] toURL() in File has been deprecated

http://docs.oracle.com/javase/6/docs/api/java/io/File.html#toURL()

Change-Id: I5ff457cdbeff0049a9e31d6aa66dd973289d5f05
Reviewed-on: https://gerrit.libreoffice.org/10506
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>