This Rhino dependency (I presume for Closure minification) will cause issues for sbt-web via js-engine. The reason being that [Trireme](https://github.com/apigee/trireme#trireme) will have its own fork of Rhino (which will ultimately be merged back to Mozilla). We could exclude the above Mozilla dependency ourselves, but I'm wondering why the pre-optimiser depends on Rhino - or is it that you've just not got to that bit of re-factoring yet...?

As a bit more background, Rhino hasn't been touched for a while and a new set of committers will probably become available.