add densitymapbox jasmine tests

Author: etpinard

test/jasmine/assets/mock_lists.js

@@ -68,7 +68,8 @@ var glMockList = [
 
 var mapboxMockList = [
     ['scattermapbox', require('@mocks/mapbox_bubbles-text.json')],
-    ['choroplethmapbox', require('@mocks/mapbox_choropleth0.json')]
+    ['choroplethmapbox', require('@mocks/mapbox_choropleth0.json')],
+    ['densitymapbox', require('@mocks/mapbox_density0.json')]
 ];
 
 module.exports = {