build.xml: use UTF-8 for encoding
build.xml: use UTF-8 for encoding

Currently scylla-tools-java fails to build when LANG is not UTF-8.
This is fix for the problem.

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

scylladb/scylla-tools-java,scylladb/scylla-tools-java,scylladb/scylla-tools-java,scylladb/scylla-tools-java