Announcing v0.5.5.

They'll also need to add our resolver explicitly, since it's a JVM project:
```scala
resolvers += scala.scalajs.sbtplugin.ScalaJSPluginInternal.scalaJSReleasesResolver
```
or else
```scala
resolvers += Resolver.url("scala-js-releases",
    url("http://dl.bintray.com/content/scala-js/scala-js-releases"))(
    Resolver.ivyStylePatterns)
```