Fix to typo in project "Build an interactive soundoard with p5js"

Closes #issue

[ ] My project tutorial topic has already been approved by the Codédex team.
[ ] My project tutorial file renders properly in mdx.
[ ] My .mdx file follows the project template, as well as what's recommended in the content guidelines.
[ ] The content written is my own, and not plagiarized from other sources.
[ ] All code written is thoroughly functional and commented (or documented).
[ ] I have already completed a self-review of the project tutorial.
[ ] I will comply with changes made or recommended by the Codédex team about my project tutorial.

codedex-io / projects