docs: fix the typo in code sample for migrating to 5.x (#461)
docs: fix the typo in code sample for migrating to 5.x (#461)

This `const { Parser, transform: { unwind, flatten } } = require('json2csv');` rightfully throws the error `TypeError: Cannot destructure property `flatten` of 'undefined' or 'null'.`

The correct version should be:
`const { Parser, transforms: { unwind, flatten } } = require('json2csv');`
zemirco/json2csv