Fixed incorrect example in mouseWheel reference.

[afthal-ahamad01]

The example incorrectly modified the X coordinate instead of the circle size.
This fix correctly centers the circle while allowing size changes.

Closes #7613

[ksen0]

Hi @afthal-ahamad01 thank you so much for noticing this, and sorry for the delayed review! Looks like it has been fixed in the source JSDoc / in the original issue processing/p5.js#7614, so I am closing the PR.

In the future, if you spot reference errors, please check the corresponding file in the p5.js repository; the main branch for p5js.org, or the dev-2.0 branch for beta.p5js.org. Please make an issue first and when it's approved for work, you are welcome to make the PR. Because it's not always obvious exactly where the fix should be, we ask for issue first before PR. Thanks you!