title: dataTaskWithRequest:completionHandler: is deprecated
body: <p>I'm using <code>AFNetworking</code> in my project to get the data from REST api.
  But when I'm using the method which described in Github I'm getting warning.</p>
  
  <p><strong>Here is my code :</strong></p>
  
  <pre><code>NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
  AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];
  
  NSURL *URL = [NSURL URLWithString:@"http://httpbin.org/get"];
  NSURLRequest *request123 = [NSURLRequest requestWithURL:URL];
  
  NSURLSessionDataTask *dataTask = [manager dataTaskWithRequest:request123 completionHandler:^(NSURLResponse *response, id responseObject, NSError *error) {
      if (error) {
          NSLog(@"Error: %@", error);
      } else {
          NSLog(@"%@ %@", response, responseObject);
      }
  }];
  
  [dataTask resume];
  </code></pre>
  
  <p>My project supports iOS 7.0 and above.</p>
  
  <p>My Xcode version 7.3.1</p>
  
  <p>Is there any way to overcome this warning?</p>