Keys In React: Improve grammar and punctuation

[Maddily]

Because

The existing explanation has minor grammatical and stylistic issues.

This PR

• Changes "rerendering" to "re-rendering" to have consistency in how the word is written throughout the lesson.
• Adjusts punctuation for smoother readability.

Issue

Closes #XXXXX

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum 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

[JoshDevHub]

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