title: No such module "PackageDescription"
body: <p>I just started with swift 3 and made a simple app in xcode using Swift 3.0 . Now i want to add a third party <a href="https://github.com/ArtSabintsev/Siren" rel="noreferrer">library</a> using Swift Package Manager . I am following installation method given in this link . I created <code>Package.swift</code> file which looks like this </p>
  
  <pre><code>import PackageDescription
  
  let package = Package (
  name : "SwiftPM",
  dependencies : [
  .Package(url: "https://github.com/ArtSabintsev/Siren.git", majorVersion: 1)
  ])
  </code></pre>
  
  <p>but i get error <code>No such module "PackageDescription"</code></p>