1.1 update

This is a very small update to fix a bug that could happen with some combinations of browser and graphics driver. The data used in generating At: the Gates maps is stored in a PNG file with color-coded pixels, and in the course of loading such a PNG file there are sometimes rounding errors on the colors, which breaks the code. I had already coded around small rounding errors but it turned out bigger ones were possible. Padding the PNG file to a power-of-two size made the math more precise, fixing the error at the cost of a pretty trivial additional amount of RAM usage.