Clarify example in first-scene.md

[winstonrc]

I think this makes it a bit clearer that the word mesh is a placeholder for the object. The way it currently reads, a novice might think following the example that they should literally use scene.remove(mesh) instead of scene.remove(cube).

[looeee]

Let me think about this one. Maybe I need to reword that section a bit.

I need to make some small updates across the site and bump the three.js version. I will try to find some time to do that later this week or early next week. I'll review this section and all your changes will go live then too.

[looeee]

@winstoncooke apologies that it's taking so long to get your updates on the live site.
It so happens to have clashed with the new Chinese translation so it's taking a bit longer to get the updates out this time.

[winstonrc]

Oops I didn't mean to delete this!

And no worries at all. Just happy to help.