for is synchronous, so you will need to require the async library. That library has an async.each() function which is an asynchronous version of forEach.
You will want to read up on it here.
Some plugins don't seem to be able to update via the ACP. Doesn't seem to be exclusive to particular plugins, but an array of them can't seem to update on different sites on different distributions that I have running.
I see he same issue as @Technowix was just going to report. Plugins that are upgradable for me seem to want to downgrade to previous version.