[PROJ] Bump CMake version for PROJ 7.0

[Howard Butler]

> On Jan 31, 2020, at 3:01 AM, Even Rouault <even.rouault at spatialys.com> wrote:
> 
> On vendredi 31 janvier 2020 08:00:18 CET Kristian Evers wrote:
>> I think a bump to 3.9 is a good idea. Per RFC3 we need the PSC to approve
>> this,
> so let's have a motion on the subject.
>> 
>> I'll start with my +1
> 
> +1

+1

I wonder if we could increase the minimum CMake requirement significantly further due to the fact that PROJ supports both CMake and autoconf for now. Do the packagers have an opinion on the topic? 

Howard