Notice: Undefined variable: gtm4wp_options

Hi,

When using the fantastic GTM plugin by Duracelltomi with WooCommerce, I found a notice message on the product page.

To reproduce this notice:
* WooCommerce plugin is activated
* Activate the debug display on site
* View a product page

Here the PHP notice:
[14-Dec-2016 09:01:15 UTC] PHP Notice: Undefined variable: gtm4wp_options in /(...)/wp-content/plugins/duracelltomi-google-tag-manager/integration/woocommerce.php on line 414

I think this behaviour is largely encountered:
https://www.google.com/search?q=Notice:+Undefined+variable:+gtm4wp_options+in+/wp-content/plugins/duracelltomi-google-tag-manager/integration/woocommerce.php+on+line+414

I suggest to add set $gtm4wp_options as global:

--- a/wp-content/plugins/duracelltomi-google-tag-manager/integration/woocommerce.php
+++ b/wp-content/plugins/duracelltomi-google-tag-manager/integration/woocommerce.php
@@ -406,6 +406,7 @@
 }
 
 function gtm4wp_woocommerce_single_add_to_cart_tracking() {
+  global $gtm4wp_options;
 	if ( ! is_single() ) {
 		return;
 	}

Please, let me know if I’m right?

Thanks.