added get single subscriber from group endpoint

Author: flowdee

src/Api/Groups.php

@@ -30,6 +30,23 @@ public function getSubscribers($groupId, $type = null, $params = [])
         return $response['body'];
     }
 
+    /**
+     * Get single subscriber from group
+     *
+     * @param $groupId
+     * @param $subscriber_id
+     * @return mixed
+     */
+    public function getSubscriber($groupId, $subscriber_id)
+    {
+        $endpoint = $this->endpoint . '/' . $groupId . '/subscribers/' . $subscriber_id;
+
+        $response = $this->restClient->get($endpoint);
+
+        return $response['body'];
+    }
+
+
     /**
      * Add single subscriber to group
      *