Fixed #73: Updated path to heatmap.js in scripts.html

Highcharts changed the paths to data.js and heatmap.js, causing our heatmaps to show black backgrounds. I updated them here so that we're not sourcing the wrong paths. See https://github.com/highslide-software/highcharts.com/commit/9f57aa7026fc317a2a53e4eccae31aab076ae8c1