Auto-publish compiler and library for Scala 2.11.0-M7.

Since the sbt plugin is essentially agnostic wrt the Scala
version, we need only publish the compiler and library for
Scala 2.11.0-M7.

A Scala.js project wanting to use Scala 2.11.0-M7 (and all
the advantages it provides to Scala.js such as SAM support
for js.FunctionN under -Xexperimental) can just specify
the following in its build file:

    scalaJSSettings

    scalaVersion := "2.11.0-M7"