WooCommerce Group Coupons 2.6.0

* Fixed several uses of coupon properties and methods for WC 3.x.

* Updated for WooCommerce 3.0.0 compatibility.
* Improved internal definitions to maintain functionality with alternate
WP_CONTENT_DIR and WP_CONTENT_URL definitions.

* Tested with WordPress 4.7.2
* Tested with WooCommerce 2.6.13
* Fixed a bug related to groups excluded from coupons.
* Added the Spanish translation.
* Removes the [Remove] link for automatically applied coupons.