What is the correct syntax for specifying multiple parameters in the url for a FileResource in a client side widget?

I get the above error when trying to add the drawing library to a modified GoogleExtensions widget:

<FileResource type="JS" url="https://maps.googleapis.com/maps/api/js?key=MY_KEY&libraries=drawing" description="" isDevelopment="false" isRuntime="true" />

I've also tried:

<FileResource type="JS" url="https://maps.googleapis.com/maps/api/js?key=MY_KEY&libraries=drawing" description="" isDevelopment="false" isRuntime="true" />

In this case, the extension gets imported fine, but then it the drawing library is not really loaded.

Thanks!

Cletus