Fix link for "How to Write an Open Source JavaScript Library"

[jaceglassbrook]

The existing link to this tutorial doesn't work because Egghead.io changed its URL scheme. To fix that, this edit does the following:

• Update the tutorial's link.
• Change the casing of the link text so it matches the tutorial on Egghead.io.

[github-actions[bot]]

:tada: This PR is included in version 4.2.5 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: