title: Extra Argument 'duration' in call
body: <p>my project is complaining that there is an "Extra argument 'duration' in call". Here is where it is occurring</p>
  
  <pre><code>required init(coder aDecoder: NSCoder) {
      workout = Workout(title: "Luke's Workout Plan", exercisePeriods: [
          ExercisePeriod(duration: 5, intensity: .High), //error
          ExercisePeriod(duration: 1, intensity: .Low),  //error
          ExercisePeriod(duration: 5, intensity: .High),  //error
          ExercisePeriod(duration: 1, intensity: .Low)  //error
          ]
      )
      super.init(coder: aDecoder)
  }
  </code></pre>
  
  <p>These variables are defined here:</p>
  
  <pre><code>struct ExercisePeriod: Printable {
  let duration: NSTimeInterval = 0
  let intensity: Intensity = .High
  
  // TODO: Make ExercisePeriod loggable
  var description: String {
      return "\(intensity.rawValue) for \(duration) seconds"
  }
  }
  </code></pre>
  
  <p>What is going wrong here?</p>