Bump netty to match Gremlin Server version.
Bump netty to match Gremlin Server version.

Bumped Netty to 4.0.28.Final.  Tested Gremlin Server SSL which seems to work nicely now.

englishtown/titan,mbrukman/titan,mbrukman/titan,thinkaurelius/titan,dylanht/titan,pluradj/titan,englishtown/titan,englishtown/titan,pluradj/titan,thinkaurelius/titan,graben1437/titan,dylanht/titan,pluradj/titan,CYPP/titan,CYPP/titan,amcp/titan,pluradj/titan,dylanht/titan,mbrukman/titan,dylanht/titan,mbrukman/titan,graben1437/titan,CYPP/titan,graben1437/titan,mbrukman/titan,graben1437/titan,CYPP/titan,amcp/titan,englishtown/titan,amcp/titan,thinkaurelius/titan,amcp/titan,thinkaurelius/titan