update deps to the latest

- eper to 0.78, same as riak develop
- riak-erlang-client to 1.4.2, which includes [cs bucket list fix](https://github.com/basho/riak-erlang-client/commit/01cdc125c1c8f14a40309f8fdb45587a3b28e37f)
- ~~webmachine to 1.10.6~~
- poolboy to 0.8.1p1
- folsom to 0.8.1