Hi,
Sorry to hear you're having some issues with the automatic installation of the GameDev Toolset.
We are currently looking into making the updating process more robust, since we have had multiple instances of similar bugs.
I will forward this bug to the Development team, thank you for posting yours.
In the meanwhile I would like to refer you to this video which explains how to install it manually. (Method 2 or 3 in this video):
https://vimeo.com/248513404 [
vimeo.com]
Paul