message: use macOS instead of macOS X
diff: @@ -5,7 +5,7 @@ Gittyup is a graphical Git client designed to help you understand and manage you
  The [stable version](https://github.com/Murmele/Gittyup/releases/stable) is available for
  - flatpak for Linux
  - 32 / 64 binary for Windows or
  -- macOS X
  +- macOS
  The [latest version](https://github.com/Murmele/Gittyup/releases/latest) is available either as pre-built for
  - flatpak for Linux,
  