Icons for xxhdpi Android devices

[newmanw]

You currently have icons for iPhone devices, but Android has higher screen resolutions.

Apple retina ~= Android XHDPI

So you are missing sprite sets for XXHDPI on android devices. I could help create those sprites but that requires access to the raw images you used for your sprites. Hopefully they are SVG such that we can create the correct size sprites without have to scale the existing png up.

Relates to #16