Add main field to package.json

[JohnstonCode]

The main field was missing from the package.json that was stopping me from requiring jschardet when bundled in a .asar

[lramos15]

Would love to see this merged as well. VS Code has a similar problem where we hardcode the entrypoint for jschardet when loading it in the web because it doesn't specify where to load it from.

[benrr101]

Azure data studio also has this issue that throws a warning. It's a one line change, can we get it pulled in?