Fix typo on phpunit tests

Author: lauramelos

tests/phpunit/bootstrap.php

@@ -32,7 +32,7 @@
 function _manually_load_plugin() {
 	$_plugin_dir = dirname( __FILE__ ) . '/../../';
 
-	require_once $_plugins_dir . '../woocommerce/woocommerce.php';
+	require_once $_plugin_dir . '../woocommerce/woocommerce.php';
 
 	require_once $_plugin_dir . 'woocommerce-gateway-amazon-payments-advanced.php';
 	require_once $_plugin_dir . 'includes/class-wc-gateway-amazon-payments-advanced-abstract.php';