Testflight app requires iOS8. How do we beta test with iOS7?

Now that Apple have integrated Tesflight into itunesconnect I thought it was time I took a look.

I have fallen at the first hurdle - when you invite a tester to test an app they are told they must have the Testflight app installed on their device, but the Testflight app requires iOS8 or later and if you have iOS7 it seems you can't be a tester.

So my question is...am i missing something and is there a way to use Apple's new Testflight beta testing system with iOS7 users?