🔨 Fix Array prototype extensions breaking construction site placement at the edges

[tiennou]

If you add something like

Array.prototype.last = function() {
  return this[this.length - 1];
}

to your bot to get additional methods on array, this piece of code ends up breaking, as the for…in loop will try running over that last key and break the check. Fix the issue by using a proper for…of loop.

Ref #126