refactor: validate array prior to adding tags on v2 forms (#8)

* rwfactor: check array type

* refactor: conditionally apply tags to subscriber

* refactor: cast array

give-activecampaign.php

@@ -431,7 +431,7 @@ public function subscribe_email( $user_info = [], $lists = [], $tags = [] ) {
 					"email"      => $user_info['email'],
 					"first_name" => $user_info['first_name'],
 					"last_name"  => $user_info['last_name'],
-					"tags"       => implode( ', ', $tags ),
+                    "tags"       => implode( ', ', (array)$tags ),
 				];
 
 				foreach ( $lists as $list ) {