camelCase event name in LMarker

[nrmncr]

Hi!

LMarker component emit event with name 'update:latLng', but according to vue2 documentation (vue2 event names) names must be in kebab-case ('update:lat-lng')

vue2-leaflet v1.2.3

[DonNicoJs]

@nrmncr thank you nice catch! I will add it to the work to be done :)