Types prevent output: source and giving tspegjs options

[fefrei]

The default way of generating a parser does not seem to typecheck in v4.2.1:

const parser = peggy.generate(grammar, {
    output: 'source',
    format: 'commonjs',
    plugins: [tspegjs],
    tspegjs: {
        customHeader: "// import lib\nimport { Lib } from 'mylib';"
    }
}

TypeScript does not like this:

This can be fixed by removing either output: 'source' or tspegjs – having both together is not allowed.