Https issue with Layerslider

Hi, Google says that the reason why our https home page is not secure  due to the fact that we are using a not secure image. When I look in the inspect function it has to do with a link to an layerslider image on the Vibes website 'http://themes.vibethemes.com/wplms/skins/default/wp-content/plugins/LayerSlider/static/admin/img/blank.gif which is a http website. And I don't understand why my layerslider wants that image? I looked in my homepage layerslider slides and I can't find a reference to this black.gif image?