title: Swift Dictionary [String:String] to NSMutableDictionary?
body: <p>I am trying to create and assign a Swift <code>Dictionary</code> of type <code>[String : String]</code> at the <code>SKSpriteNode</code> property <code>userData</code> which requires an <code>NSMutableDictionary</code>. When I try this I get the error:</p>
  
  <pre><code>'[String : String]' is not convertible to 'NSMutableDictionary'
  </code></pre>
  
  <p>Can anyone point me in the right direction?</p>
  
  <pre><code>    // USER DATA
      var dictionary: [String : String] = Dictionary()
      dictionary["Orbit"] = orbit
      dictionary["Zone"] = zone
      dictionary["Impact"] = impact
      var foundationDictionary = dictionary as NSMutableDictionary
      neoSprite.userData = foundationDictionary
  </code></pre>