Map field doesn't use api key

I'm using the example code from the documentation to add a map field and provided my own api key, but the plugin doesn't add that key at the end of the Google maps url. The current url looks this way:

https://maps.google.com/maps/api/js?v=3.exp&ver=4.9.9

The expected result is something like this:

https://maps.googleapis.com/maps/api/js?key=XXXXXXXXXXXXXXXXXXXXXXXXXx&ver=4.9.9