Updating Riak-JS and dependencies

[Neamar]

To sum up:

• Using riakpbc 2.1, dropping support for node 0.8
• Fix Travis CI
• Cleaner dependencies

[Neamar]

Also, using riakpbc 2.1, we had to drop support for non-streams on protobuf for keys and buckets retrievals.

The lib will be updated to riak-js@1.0.0 to reflect all those breaking changes.