Improve clarity of lightFalloff() example

[JetStarBlues]

In the current example, the translations to place the spheres are done globally (instead of using push and pop). As a result, the light positions are affected by these translations.

As a consequence of this, the color of the rightmost sphere is affected more by the light position than by falloff.

This is what the two spheres look like in the current example if the lines setting lightFalloff() are commented out:

What should happen instead is that both spheres are equally lit. Here is what they look like with lightFalloff() commented out in the proposed example:

In the proposed changes (live version here), the difference between the two spheres becomes attributable to falloff only.

Change as docs:

[stalgiag]

Great change!