fix(typings): ensure compatibility with TypeScript 3.x
fix(typings): ensure compatibility with TypeScript 3.x

Labeled tuple elements were added in TypeScript 4.0.

Reference: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-0.html#labeled-tuple-elements

Related: https://github.com/socketio/socket.io/issues/3916

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