lookup endpoints: use a constant on the example, it's prettier

Author: Marcel Corso

examples/lookup-hlr-view.php

@@ -17,7 +17,7 @@
     $poolCount = 10;
     while($poolCount--) {
         $hlr = $MessageBird->lookupHLR->read($Hlr->msisdn);
-        if ($hlr->status != 'sent') {
+        if ($hlr->status != \MessageBird\Objects\Hlr::STATUS_SENT) {
             // we have something
             var_dump($hlr);
             break;