title: scanForPeripheralsWithServices:return result twice on the same peripheral
body: <p>I use the below code  </p>
  
  <pre><code>[centralManager scanForPeripheralsWithServices:serviceUUIDArray 
           options:[NSDictionary dictionaryWithObject:[NSNumber numberWithBool:NO] 
           forKey:CBCentralManagerScanOptionAllowDuplicatesKey]] 
  </code></pre>
  
  <p>to scan a perpheral device, then the result return twice on the same peripheral. How to return one? Thanks.</p>