message: update CUDA requirements in README
diff: @@ -45,7 +45,7 @@ For Ginkgo core library:
  The Ginkgo CUDA module has the following __additional__ requirements:
  -* _CUDA 9.0+_
  +* _CUDA 9.2+_
  * Any host compiler restrictions your version of CUDA may impose also apply
  here. For the newest CUDA version, this information can be found in the
  [CUDA installation guide for Linux](https://docs.nvidia.com/cuda/cuda-installation-guide-linux/index.html)
  @@ -87,7 +87,7 @@ __NOTE:__ Need to add `--autocrlf=input` after `git clone` in _Cygwin_.
  The Ginkgo CUDA module has the following __additional__ requirements:
  -* _CUDA 9.0+_
  +* _CUDA 9.2+_
  * _Microsoft Visual Studio_
  * Any host compiler restrictions your version of CUDA may impose also apply
  here. For the newest CUDA version, this information can be found in the
  