title: AltBeacon Library shows beacons only once and then stops showing them
body: <p>I experience an issue and can reproduce it on different devices with different Android OS. 
  I get the expected behaviour with iBeacon scanning for the first time. When I scan the next time I get no Beacons. The result list in delegate is empty. I printed a count on the setRangeNotifier with the size of the beacons but apparently after it only shows the beacons size to be 1 for the first time after which it continually displays a 0. </p>
  
  <pre><code>beaconManager.setRangeNotifier(new RangeNotifier() {
      @Override
      public void didRangeBeaconsInRegion(final Collection&lt;Beacon&gt; beacons, Region region) {
         Log.d("Beacons count",beacons.size());
      }
  });
  </code></pre>
  
  <p>Output:
  Beacons Count 1
  Beacons Count 0
  Beacons Count 0
  Beacons Count 0</p>
  
  <p>My ranging period and scanning period is as below</p>
  
  <pre><code>beaconManager.setBackgroundScanPeriod(1000l);
  beaconManager.setBackgroundBetweenScanPeriod(31000l);
  </code></pre>