Update classes/integrations/google-analytics/class-wc-google-analytics.php

Added use of product SKU to "Add to cart" event.
Update templates/loop/add-to-cart.php

Added data-product_sku attribute to allow SKU tracking in analytics from shop loop.
Update classes/integrations/google-analytics/class-wc-google-analytics.php

Added SKU tracking for shop loop
Merge pull request #2441 from yitzchak/patch-2

Update classes/integrations/google-analytics/class-wc-google-analytics.p...