Mailchimp for WordPress Premium 4.9.3

- Reports: Fix JS issue when viewing chart.

- Update classnames to work with Mailchimp for WordPress version 4.8.4 and up.
- Rewrite CSS selectors for optimized performance.
- Fix order of arguments for function call to `join` because of PHP 7.4 deprecation.
- E-commerce: Optimize tracker.js for file size by getting rid of third-party dependency.
- E-commerce: Add `defer` attribute to cart.js and tracker.js `<script>` elements.

**Additions**

- [User Sync](https://www.mc4wp.com/kb/what-does-mailchimp-sync-do/) feature, which allows you to synchronize WordPress user fields with subscriber fields in Mailchimp and vice versa.

**Improvements**

- E-commerce: Capture `billing_postcode` field for guest customers abandonding the checkout form.
- E-commerce: Reduce JavaScript file size for abandoned cart tracking by 25%.
- Licensing: Show notice when plugin is running on a live website without an active license.
- Forms: Reduce JavaScript file size for enhancing forms with AJAX functionality.