Demo does not work: https cdn for js/css-files

[tobiaskauer]

The demos at https://leflet.github.io/Leaflet.heat/demo/ and https://leaflet.github.io/Leaflet.heat/demo/draw.html do not work.

github.io forces a https connection while leaflet.js and leaflet.css are loaded via http. this results in a blank page for most browser configurations.