sbt: Add finagle-core/test as a dep of finagle-thriftmux
sbt: Add finagle-core/test as a dep of finagle-thriftmux

Summary: Problem:
finagle-thriftmux sbt is mising a denpendency.

Solution:
Add it.

JIRA Issues: CSL-5990

Differential Revision: https://phabricator.twitter.biz/D137648

luciferous/finagle,luciferous/finagle,twitter/finagle,twitter/finagle,luciferous/finagle,twitter/finagle,luciferous/finagle,luciferous/finagle,twitter/finagle,luciferous/finagle,twitter/finagle