Fix `main` entry in `package.json`

[AStoker]

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You want to:

• report a bug
• request a feature

Current behaviour

The main entry is missing the required extension inside the package.json file (https://nodejs.dev/learn/the-package-json-guide#main)

Steps to reproduce (if the current behaviour is a bug)

• Open package.json.
• Observe missing extension in main entry

This causes various tools to fail that automatically try and find the entry file when scanning node modules.

Expected behaviour

The main entry should have an extension

Setup

• OS: Mac OS 11.0.1 Beta
• browser: Safari 14.0.1
• engine.io version: 4.0.1

Other information (e.g. stacktraces, related issues, suggestions how to fix)