We recently upgraded to 2018.1.6f, and with that I recommended folks install and start using Unity hub, as we have a few different unity versions being used by the project in different stages of being shipped out to our players. Hub is great for making sure you open those different versions of the project in the right version of Unity!
… if you have the right version of Unity installed already.
Unfortunately, it looks like only the latest, latest version per minor version of a Unity release can be installed manually from the hub. When I told people to use Hub, they could install 2018.1.6 from it. Now, they have to go download it manually, then locate it manually, before Hub is useful, because only 2018.1.8 is available in the hub.
It’d be great if clicking on a project that is set to a Unity version you don’t have installed would also present you with the option to install that version.