Version: rss-parser@3.13.0

The following code works as expected but fails to compile under Typescript:

import Parser from 'rss-parser';
const parser = new Parser({
 customFields: {
 feed: [['dc:language', 'language']]
 }
});

Typescript error: Type '[string, string]' is not assignable to type 'string | number'. ts(2322)

It feels like this should be allowed for a few reasons:

• The README reads like it should work (no special case to say feed is more restricted that item)
• The default fields defined in lib/fields.js use these types of values (eg ['dc:publisher', 'publisher'])
• It does appear to work correctly when ignoring the Typescript error