finagle: Fix sbt build
finagle: Fix sbt build

Problem

Finagle is not using the correct version of the scrooge-sbt-plugin.

Solution

Use the current version, 4.6.0, when building on master.
Use version 4.6.0-SNAPSHOT if building on any other branch.

RB_ID=821061

twitter/scrooge,thirstycrow/scrooge,thirstycrow/scrooge,thirstycrow/scrooge,twitter/scrooge,twitter/scrooge,thirstycrow/scrooge,thirstycrow/scrooge,twitter/scrooge