vscode extension cSpell is so helpful

[zhouhanseng]

It is so happy to avoid typo by this extension. https://marketplace.visualstudio.com/items?itemName=streetsidesoftware.code-spell-checker

I find three typos just now!

[Jack-Works]

IIRC this plugin is in our recommended extension list.

The third one is not typo, it a feature of vscode.

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