Updated client.js for clients-291
Updated client.js for clients-291

Callback is now passed explicitly instead of inside options.

GabrielNicolasAvellaneda/riak-nodejs-client,basho/riak-nodejs-client,authbox-lib/riak-nodejs-client,GabrielNicolasAvellaneda/riak-nodejs-client,authbox-lib/riak-nodejs-client,basho/riak-nodejs-client