Fix dispatcher method that was removed

Author: BrianHigby

src/PositionObserver.php

@@ -157,6 +157,6 @@ protected function firePositioningEvent($query)
      */
     protected function firePositionedEvent(Model $model)
     {
-        $this->events->fire('eloquent.positioned: '.get_class($model), [$model]);
+        $this->events->dispatch('eloquent.positioned: '.get_class($model), [$model]);
     }
 }