Fix types for list_keys/2 and list_keys/3
Fix types for list_keys/2 and list_keys/3

rhumbertgz/riak-erlang-client,groovenauts-erlang/riak-erlang-client,paulperegud/riak-erlang-client,linearregression/riak-erlang-client,SiftLogic/riak-erlang-client,pma/riak-erlang-client,jmayfield74/riak-erlang-client,esl/riak-erlang-client,GabrielNicolasAvellaneda/riak-erlang-client,inaka/riak-erlang-client