duplicate `.editorconfig` config, typo, sample code and grammar

[dev-itsheng]

Yes, I promise I've read the Contributions Guidelines (please feel free to remove this line).

Specifically quoting these guidelines regarding typos:

Typos?

Please don't worry about minor text typos. These will almost certainly be caught during the editing process.

If you're going to submit a PR for typo fixes, please be measured in doing so by collecting several small changes into a single PR (in separate commits). Or, just don't even worry about them for now, because we'll get to them later. I promise.

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Please type "I already searched for this issue":

I already searched for this issue

Edition: (pull requests not accepted for previous editions) 2

Book Title:

Chapter: 1 & 2 & A & 4 & 5

Section Title: many

Topic:

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I found an issue of sample code, but found that has been pointed in https://github.com/getify/You-Dont-Know-JS/pull/1770, so I didn't fix.

[getify]

👀

[getify]

The changes to the markup around "NOTE" elements is unnecessary.

[dev-itsheng]

The changes to the markup around "NOTE" elements is unnecessary.

When I modified the text before, it triggered the editor's Markdown table formatting, which caused changes around NOTE:.

The amendments to that section have been withdrawn.