Add capability_type to product_variation

By default the product_variation has `capability_type = 'post'` which means that users need `edit_post` capability to edit. This change will make variation capabilities consistent with products, ie: `edit_product`

includes/class-wc-post-types.php

@@ -269,6 +269,7 @@ class WC_Post_types {
 					'public'       => false,
 					'hierarchical' => false,
 					'supports'     => false
+					'capability_type' => 'product'
 				)
 			)
 		);