Docs reference non-existent WheelJoint.js example

[rgov]

planck.js/docs/pages/joint/wheel-joint.md

Lines 2 to 5 in 4b6d6ec

	## Wheel Joint
	The wheel joint restricts a point on bodyB to a line on bodyA. The wheel
	joint also provides a suspension spring. See WheelJoint.js and Car.js
	for details.

There is no WheelJoint.js.

There is WheelJoint.ts which is the implementation of the joint. Is that what it means? Car.js is an example, it so it sounds like WheelJoint.js is an example (like there is MotorJoint.js).