JS exercises README: change shortcuts to kbd format

[ManonLef]

Because

We recently updated the style-guide to use <kbd> element formatting on keyboard shortcuts. There was one shortcut to be updated in this readme.

This PR

• convert keyboard shortcut to correct styling for this repo's readme

Issue

Related to #25715

Additional Information

• I have ignored other style issues PR dedicated to the keyboard shortcuts

Pull Request Requirements

• I have thoroughly read and understand The Odin Project Contributing Guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide

[xandora]

Looks good to me.