Circle collision for Bird

[matiasvlevi]

Bird/Pipe collision assumes the bird has a square shape, when in reality we should be applying circle collision.

Here is a snippet from the current Pipe/bird collision method.
This method returns true when the bird is colliding with a Pipe.

flappy-bird/public/classes/pipe.js

Lines 33 to 40 in d18635d

	isColliding(bird) {
	return (
	wnx / 2 > this.x - 3 &&
	wnx / 2 < this.x + this.width + 3 &&
	(bird.y < this.y - this.gapSize + 3 ||
	bird.y > this.y - 3)
	);
	}

NOTE:

Ideally we would move this method in the Bird class, and implement a system tracking the nearest Pipe instance. Only 1 Pipe instance should check collision at a time as mentionned in #2