Problem was that the Google vendor class in your install used the previous Google's version naming convention (no uppercase first) so the system wasn't able to find Config.php or Auth folder. This problem was triggered because you used Windows server in the past and in Windows there is no such thing as a differentiation between lowercase and uppercase for files and folders.
So when you moved to nginx, the system was all wrong due to this. Even in Windows it was wrong because the Windows file system doesn't make a difference in lower/upper cases so it didn't updated "auth" to "Auth" or "io" to "IO" and you carried that bug to nginx. As a side note, I always use lowercase for files but Google in is huge wisdom uses uppercase first letter (go figure).
Thing is that this could get fixed by simply fooling the update system (put 3.6.9 in chevereto_version_installed then run /update) or just by putting the missing uppercases (I did this).
This is one of the many reasons why I don't encourage to use Windows servers. Anyway, your website is fixed now.
