SSL issue
We've been receiving a lot of MineOS installation issues related to outdated SSL certificates lately.
The error looks like this:
This happens due to using of very ancient java 8 releases that contains expired SSL certificates related to github.com where MineOS is downloaded from.
If you are playing in a single mode, simply download latest available java 8 release and make sure that your launcher is using this version. You can check java version used by minecraft instance by pressing F3 and looking at the top right corner:
If you are playing on a public server, then just deal with it. There is nothing to do unless server owner will update java on a server side.