color path lines for each robot

[Elucidation]

all paths are the same color, would be nice if each robots path gets a unique color

[Elucidation]

let path_color_offset = 1.0 /robots.length;
...
svg_path.style.stroke = `rgba(${250 - 250*path_color_offset*idx}, 138, 50, 0.466)`;

Line 164 in visualizer.js will do it