add commonjs annotation to package.json

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I'm working on making this tool compatible with deno and bun for a personal project. It looks like I'm not the only one who would like to add that support (See: #1108)

Modern JS standards suggest either using a .cjs extension or a module type declaration on a package to know whether something is a commonjs module or an esm module. See: https://nodejs.org/api/packages.html#packagejson-and-file-extensions

This change adds the missing "type": "commonjs" annotation to the package.json file to allow deno to run the files correctly.

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@benibenj, do you know what the stalled vsce OSS check is? Not sure if I missed a setup step before I can make contributions