I’m sure Check For Updates will tell you when 2018.2 comes out. I don’t believe the Check For Updates window reports when minor updates are available, which occur every few weeks. These updates used to be the patch releases, and Check For Updates never reported new patch releases. So I think it is working as designed.
Unity has made notification of new updates by email available. You just need to go to these threads, click “Watch Thread” and select the radio button “and receive email notifications.”
Tech Release build announcements: (Currently 2018.x.x)
LTS Release build announcements: (Currently 2017.4.x)
Patch Release build announcements (Legacy patch releases for 5.x.xpx, 2017.1.xpx, & 2017.2.xpx)