deletedvclock wrong in docs

[lixen]

http://docs.basho.com/riak/kv/2.2.3/developing/usage/deleting-objects/

[{deleted_vclock}] should be [deletedvclock]

see

https://github.com/basho/riak-erlang-client/blob/9167ad627348d4995ef60c93c63ce39a16eb9735/src/riakc_pb_socket.erl#L1574