Update webgl_shaders_ocean.html

[skyclouds2001]

Description

THREE.PMREMGenerator.prototype.fromScene method receive a scene param of Scene instance, see PMREMGenerator docs.
Even though, this incorrect param seem not to influence the final behavior of this example.

See https://threejs.org/examples/#webgl_shaders_ocean

[Mugen87]

Unlike WebGLRenderer.render(), PMREMGenerator.fromScene() expects an instance of Scene. That's because the internal _sceneToCubeUV() method sets the background property at the end of its implementation.

three.js/src/extras/PMREMGenerator.js

Line 379 in a0cb769

scene.background = background;

In the example, the sky object ends up with an undefined background property. Nothing breaks because of this but after all it is not ideal.

However, I don't think the PR is correct in its current form since the scene you are using is the same scene that holds the water and box. It's more correct to use a second scene, add the sky to it, execute PMREMGenerator.fromScene() and then add the sky back to its original scene. Or alternatively, you just use one scene but set the visible property of the water and box to false before fromScene() runs (and then restore the values).

[skyclouds2001]

Emmm, you are right. I'll update my pull request later.

[Mugen87]

Slightly updated the PR.