adding user_id field with every event and people updates

lib/Producers/MixpanelEvents.php

@@ -27,10 +27,10 @@ public function track($event, $properties = array()) {
 
         // if no time is passed in, use the current time
         if (!array_key_exists('time', $properties)) $properties['time'] = time();
-
         $params['event'] = $event;
         $params['properties'] = array_merge($this->_super_properties, $properties);
 
+
         $this->enqueue($params);
     }
 
@@ -120,7 +120,8 @@ public function getProperty($property) {
      * @param string|int $user_id
      */
     public function identify($user_id) {
-        $this->register("distinct_id", $user_id);
+        $this->register('distinct_id', $user_id);
+        $this->register('$user_id', $user_id);
     }
 
 
@@ -161,4 +162,4 @@ public function createAlias($original_id, $new_id) {
     function _getEndpoint() {
         return $this->_options['events_endpoint'];
     }
-}
+}

lib/Producers/MixpanelPeople.php

@@ -18,6 +18,7 @@ private function _constructPayload($distinct_id, $operation, $value, $ip = null,
         $payload = array(
             '$token' => $this->_token,
             '$distinct_id' => $distinct_id,
+            '$user_id' => $distinct_id,
             $operation => $value
         );
         if ($ip !== null) $payload['$ip'] = $ip;