title: generic parameter could not be inferred (swift 3)
body: <p>I use AFNetworking and Mantle library on my project. I decided to migrate swift 3. And I got this error -> "generic parameter 'ResponseType' could not be inferred" on getSources function </p>
  
  <p>ApiBaseHelper.swift</p>
  
  <pre><code>class func GET&lt;ResponseType&gt;(url: String, parameters: AnyObject!, path: String!, callback: @escaping (_ operation: AFHTTPRequestOperation?, _ result: [ResponseType]?, _ error: Error?) -&gt; ()) -&gt; AFHTTPRequestOperation! where ResponseType: MTLJSONSerializing, ResponseType: MTLModel{
  
      return NetworkManager.sharedInstance!.get(url, parameters: parameters,
          success: {(operation: AFHTTPRequestOperation?, result: Any?) -&gt; Void in
              self.parseResponse(response: result as AnyObject!, operation: operation, path: path, callback: callback)
          },
          failure: { (operation: AFHTTPRequestOperation?, error: Error?) -&gt; Void in
              print("error get request =&gt; \(error)")
              callback(operation, nil, error as Error?)
          }
      )
  }
  </code></pre>
  
  <p>ApiHelper.swift</p>
  
  <pre><code>class func getSources(_ callback: @escaping (_ operation: AFHTTPRequestOperation?, _ contents: [Source]?, _ error: Error?) -&gt; ()) {
      var params = [String: AnyObject]()
      params["apiKey"] = API_KEY as AnyObject?
      let url = String(format: SOURCE_PATH)
  //generic parameter 'ResponseType' could not be inferred
      GET(url: url, parameters: params as AnyObject!, path: "sources") { (operation: AFHTTPRequestOperation!, result: [Source]?, error: Error!) -&gt; () in
          callback(operation, result, error)
      }
  }
  </code></pre>