message: Update README.md
  Fix download link to point to latest version
diff: @@ -16,7 +16,7 @@ meshoptimizer is hosted on GitHub; you can download the latest release using git
  git clone -b v0.18 https://github.com/zeux/meshoptimizer.git
  ```
  -Alternatively you can [download the .zip archive from GitHub](https://github.com/zeux/meshoptimizer/archive/v0.15.zip).
  +Alternatively you can [download the .zip archive from GitHub](https://github.com/zeux/meshoptimizer/archive/v0.18.zip).
  The library is also available as a package ([ArchLinux](https://aur.archlinux.org/packages/meshoptimizer/), [Debian](https://packages.debian.org/libmeshoptimizer), [Ubuntu](https://packages.ubuntu.com/libmeshoptimizer), [Vcpkg](https://github.com/microsoft/vcpkg/tree/master/ports/meshoptimizer)).
  