Document the notation for invalidating nested array fields

[dandv]

At https://mongoosejs.com/docs/api/document.html#document_Document-invalidate, the path parameter is documented as,

path «String» the field to invalidate

What is the format for nested array fields? array.2.field, array[2].field?

[vkarpov15]

array.2.field. We don't currently support square bracket notation.