Fix distance between two points formula

[AymeneBahmed]

the method:

distance(x1, y1, x2, y2) {
return Math.sqrt((x1 - x2) * (x1 - x2) - (y1 - y2) * (y1 - y2));
}

should be:

distance(x1, y1, x2, y2) {
return Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}