Rotate bullets position in rotation of gun

[alexandernst]

Answering to my own question: http://plnkr.co/edit/nBoIiwjEA5M93OUawayX?p=preview

    this.input.on("pointermove", function(pointer) {
      var angle = Math.atan2(pointer.y - this.gun.y, pointer.x - this.gun.x) * 180 / Math.PI;
      this.gun.angle = angle;
    }, this);