Guys what you have to do is the following:
1. Uninstall Twitch
2. Click on the install menu and click "advanced" and change the path to like: C:\Twitch
3. Then, open twitch, go to the 3 bars at the top left, click file, Settings and click "Minecraft".
4. Change the Location of Minecraft to the path you put at the installation. (C:\Twitch)
5. Go to your desktop and find your "Minecraft Launcher", the normal launcher for minecraft, click with the right mouse button and click on "Open File Location"
6. Copy the "MinecraftLauncher.exe"
7. Go to the folder you put at the installation (C:\Twitch)
8. Go "Install" Folder
9. Paste the "MinecraftLauncher.exe" and change the name to "minecraft.exe".
Try to install the mod now on Twitch.
It should work, it did it for me.