Xamarin Forms comptaibility

Hi,

I've not coded much in X.Forms up to this point, so this question might not make much sense but all of a sudden the availability of the iOS OS versions to simulate with have become reduced from 7.1 and 8.1, to just 8.1 - why would 7.1 disappear?

I'm coding in Visual Studio connected to a mac where the simulator is running.

The only thing I've done is implement the MessagingCenter - I don't know if it's a coincidence but since I made use of the MessagingCenter, 7.1 seemed to disappear?

Any info that would help me identify how to get 7.1 back would be useful.

Thanks