Add support for npm 7

[diogoazevedos]

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After upgrading npm to 7, the npm install started to fail because the dirs libexec/lib doesn't exist. On Homebrew/homebrew-core#63170 I added the mkdir_p libexec/"lib" to 2 formulas, but probably this will be necessary again for other formulas.

These lines should be removed later.

[chenrui333]

lgtm

[MikeMcQuaid]

Thanks so much for your first contribution! Without people like you submitting PRs we couldn't run this project. You rock, @diogoazevedos!