title: Subscribe returning Void instead of AnyCancelable
body: <p>I currently have a publisher with the type of <code>AnyPublisher&lt;[MyClass], Error&gt;</code> to which I'm attempting to attach a subscriber and capture the resulting <code>AnyCancelable</code>. Xcode's autocomplete says I should be able to do this, but when the code is actually entered, I encounter a compiler error saying that the returned type isn't <code>AnyCancelable</code>, but <code>()</code></p>
  
  <p>Here's an example of my code:</p>
  
  <pre><code>let networkController = NetworkController()
  let viewState = MyViewState()
  
  let publisher: AnyPublisher&lt;[MyClass], Error&gt; = networkController.createPublisher()
  let cancelable: AnyCancellable = publisher.subscribe(viewState)
  Cannot convert value of type '()' to specified type 'AnyCancellable'
  </code></pre>
  
  <p>My goal here is to wrap an existing async function, which could be called numerous times, in the Combine Framework, so that I can have a nice way of having the request get canceled when it's reassigned, like so:</p>
  
  <pre><code>... self.cancelable = cancelable
  </code></pre>