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

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

Change-Id: I4322254d04e3ccf894acebf8b71de6f51e0a110a
Reviewed-on: https://gerrit.libreoffice.org/10467
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>