The method bindLabel
from the plugin Leaflet.label is deprecated but its functionality was included in Leaflet core from version 1.0 using tooltip.
This should work within your code:
var marker = L.marker([ latitude, longitude ], {
icon : iconInfo,
iconAnchor: [10, 10],
labelAnchor: [6, 0]
}).bindTooltip(displayingText, {
direction: 'bottom',
noHidepermanent : true
}).addTo(leaf_map);