Plugin broken, bug fixes

This plugin has several bugs that prevent it from working.

In the file: front/class-wc_update-variation_in-cart_ck.php

1. The bug: makes direct calls to WooCommerce class WC_Product_Factory (via wc_get_product()) for product id, but that is no longer a valid way to obtain product id as of WooCommerce version 3.

The fix: search for all references to $product_woo_ck->id and replace with $product_woo_ck->get_id() (lines 215, 364, 368)

2. The bug: references a non-existent variable, $attribute_keys on line 254.

The fix: Rename variable to $attributes

The two fixes above at least allow the variations dropdown to actually appear.

There are still more bugs in the submission part once you change the variation, and I gave up trying to fix it.