Fix typo (a -> an)

pkg/controller/volume/persistentvolume/pv_controller.go

@@ -365,7 +365,7 @@ func (ctrl *PersistentVolumeController) syncUnboundClaim(claim *v1.PersistentVol
 				glog.V(4).Infof("synchronizing unbound PersistentVolumeClaim[%s]: volume is unbound, binding", claimToClaimKey(claim))
 				if err = checkVolumeSatisfyClaim(volume, claim); err != nil {
 					glog.V(4).Infof("Can't bind the claim to volume %q: %v", volume.Name, err)
-					//send a event
+					//send an event
 					msg := fmt.Sprintf("Cannot bind to requested volume %q: %s", volume.Name, err)
 					ctrl.eventRecorder.Event(claim, v1.EventTypeWarning, events.VolumeMismatch, msg)
 					//volume does not satisfy the requirements of the claim