lerpVectors( v1, v2, alpha ) {

		this.x = v1.x + ( v2.x - v1.x ) * alpha;
		this.y = v1.y + ( v2.y - v1.y ) * alpha;
		this.z = v1.z + ( v2.z - v1.z ) * alpha;

		return this;

	}
Linearly interpolates between the given vectors, where alpha is the percent
distance along the line - alpha = 0 will be first vector, and alpha = 1 will
be the second one. The result is stored in this instance.

@param {Vector3} v1 - The first vector.
@param {Vector3} v2 - The second vector.
@param {number} alpha - The interpolation factor, typically in the closed interval `[0, 1]`.
@return {Vector3} A reference to this vector.