CMake version

[erincatto]

I'm seeing this all the time lately using enkiTS via CMake.

CMake Deprecation Warning at build/_deps/enkits-src/CMakeLists.txt:1 (cmake_minimum_required):
Compatibility with CMake < 3.5 will be removed from a future version of
CMake.

Update the VERSION argument value or use a ... suffix to tell
CMake that the project does not need compatibility with older versions.

It would helpful to bump the version to 3.5. I tested this and it seems fine. I'd submit a PR, but it is a one line change.

[dougbinks]

Thanks for this issue report - I'm happy to receive a PR if you want your name in the commit log, but I'm equally happy just to make the change myself.

[erincatto]

See #126