dxvk verb: use Github API to get latest release
dxvk verb: use Github API to get latest release

 * use w_get_github_latest_release() to get latest release
 * use winetricks local variable naming convention
 * fixes: https://github.com/Winetricks/winetricks/issues/1277
 * update Vulkan requirements

Winetricks/winetricks,Winetricks/winetricks