title: sbt-assembly not working for scala 2.12.1
body: <p>My project build, when using scalaVersion to be 2.11.8. When I switch to scalaVersion 2.12.1, I get the error that the symbol <code>assembly</code> in <code>mainClass in assembly := ...</code> cannot be found. Is <a href="https://github.com/sbt/sbt-assembly" rel="nofollow noreferrer">https://github.com/sbt/sbt-assembly</a> not working with scala 2.12.1 yet?</p>
  
  <p>So</p>
  
  <pre><code>scalaVersion in ThisBuild := "2.11.8",
  </code></pre>
  
  <p>works, but</p>
  
  <pre><code>scalaVersion in ThisBuild := "2.12.1",
  </code></pre>
  
  <p>does not work.</p>