When trying to update from v3.7.4 to v3.7.5 (ee update) I get the follwing error:
Downloading update script Unable to download file, /tmp/eeupdate20180405-234952
I get the same thing.
You can run the install command itself to update to the new version.
wget -qO ee rt.cx/ee && sudo bash ee
See this thread for more details. Ee update fail