Raise netty version to 4.0.56.Final
Raise netty version to 4.0.56.Final

This solves the problem of IntObjectHashMap not supporting
negative keys in the previous version (4.0.23.Final), in sstableloader.

Problematic method in 4.0.23.Final:
https://github.com/netty/netty/blob/netty-4.0.23.Final/common/src/main/java/io/netty/util/collection/IntObjectHashMap.java#L312

Fixed method in 4.0.56.Final:
https://github.com/netty/netty/blob/netty-4.0.53.Final/common/src/main/java/io/netty/util/collection/IntObjectHashMap.java#L356

Signed-off-by: Piotr Jastrzebski <2c0eb4a25a7cde333ff2d0860cb06051925fd74f@scylladb.com>
Message-Id: <2c07489a1de83c0dd58d062d0a028b6b77efd066.1534839566.git.2c0eb4a25a7cde333ff2d0860cb06051925fd74f@scylladb.com>

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