MapHeightNodeShader: rename vUv to vMapUv (three >= r151)

[Avnerus]

Hi,

Thank you for this library!
I tried using HEIGHT_SHADER with threejs r164 and got an error that vUV is undeclared.
I checked around and found that in r151 vUV was renamed to vMapUv.
This PR fixes the error for me.

/Avner

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[tentone]

Thanks a lot! LGTM

Merged!