Riak2.0

This closes #22
The riak2.0 driver uses java Future to perform operations. There are various changes in the API. Read this blog entry. http://bit.ly/1v50Hcp

This fix moves `scalaz to 7.1`, and complies with `scala 2.111 as well. 
`mockito` is removed as the `riak2.0` driver uses a builder approach to create stuff and the classes aren't exposed.

*Would need help on suggestion on improving the `testcases`*. Right now the basic we use are tested.

* fetch
* fetch index
* store
* ping
* listbuckets
* store with index

The specs are broken to down to their functionality.