Use as short version numbers as is relevant for each browser

In the browser picker, we use the full version numbers, which isn't very important to show, and means that we get longer lists where it's harder to find what you're looking for, especially if you're looking for a specific version and platform.

Should probably be consistent with https://github.com/w3c/wptdashboard/issues/494 (and https://github.com/w3c/wptdashboard/issues/493).