Use backticks rather than concatenation

[eyalroz]

In modern Javascript, we can write:

let foo = `Voxel coordinates are (${x}, ${y}, ${z})`;

while in the past we had to write this add

let foo = 'Voxel coordinates are (' + x + ', ' + y + ', ' + z + ')';

the former is easier to type and less easy to get confused about. Let's use it then.