Fix Travis riak_pb installation hack again.
Fix Travis riak_pb installation hack again.

TouK/vumi,harrissoerja/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,harrissoerja/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi