Use Travis CI's new container-based infrastructure

Problem

Travis CI just announced a new container-based infrastructure that provides
faster builds, etc., and can be enabled by disabling sudo in the Travis config.

Solution

We don't need sudo for any of these projects, so we can disable it. I've also
fixed a few minor issues with versions in the Travis configuration for scrooge,
finagle, and twitter-server.

RB_ID=547354