Possible anachronism in CMake `target_include_directories`

When trying to compile, [line 29 of the CMake file](https://github.com/arrayfire/arrayfire-ml/blob/master/CMakeLists.txt#L29) was giving me trouble. Changing the included item from `ArrayFire::af` to `af` solved the issue. I'm using CMake 3.10.2

See also:
1. https://cmake.org/cmake/help/latest/command/target_include_directories.html
2. https://gitlab.kitware.com/cmake/cmake/issues/15689

Comece na linha 29 de CMakeLists.txt e reproduza o problema de compilação com o CMake 3.10.2. Compare as formas ArrayFire::af e af usando a documentação vinculada do CMake e a issue 15689. Considera-se concluído quando o projeto compilar sem exigir o workaround relatado.

Escrita pelo modelo de indexação a partir do texto da issue.