title: When can incremental version number of dependency in sbt be left out?
body: <p>What determines when I can omit the incremental version number of a dependency in sbt?</p>
  
  <p>For dependencies on Scala, I find that I can't omit the incremental number. I need to specify <code>2.10.3</code> or <code>2.10.4</code> for example, and a mere <code>2.10</code> does not work.</p>
  
  <p>For dependencies on <a href="http://www.scalatest.org/" rel="nofollow">ScalaTest</a>, I found that for v2.0 I can specify just <code>2.0</code>, but for 2.1 I need to specify <code>2.1.0</code>.</p>
  
  <p>Is this determined by the author of the library in some way?</p>