I believe we're using version 16 of admob at the moment, we used to use the latest but there was a breaking change introduced in 17. So it got "temporarily" set to 16. It's been pending on my TODO list to make the plugin work with 17, and go back to always using the latest version. But there wasn't an urgent reason ( other than it not working I can't remember any notable changes ).
By the looks of it there isn't any steps other than use the latest SDK that we need to take. I'll update my TODO list and try to get around to it sooner rather than later.