Revert "Rename web-dev-javascript-book.txt to web-dev-javascript-book.md"

This reverts commit 1b4c4bfa49708e3cb9364ae884dda044a39f2e05.
Revert "Update web-dev-javascript-book.txt"

This reverts commit bb75f748ca2c304a0c391d8f66487a56d3b1de8c.