Build ios occur error with package service

Hi all ,

I have an issue with build service
When i add to config.xml , and build with ionic package service , it will be fail . Every thing work fine after i remove this plugin .
Here is my config :

 <plugin name="" spec="~1.3.9">
   <variable name="API_KEY_FOR_ANDROID" value="AIzaSyCcheAIlg-TcJMIpvLqzHlddbyXWK*"/>
   <variable name="API_KEY_FOR_IOS" value="AIzaSyDuix5Id7SGgaP7Fa3AWhdE98ozx*"/>

Thanks for you time