Apple has just pushed an update to the data used by Gatekeeper, bringing its version number to 156, dated 30 October 2018.
Apple provides no details as to what changes this update brings, but it is normally expected to include recent revocations of security certificates used in signing software.
You can check whether this update has been installed by opening System Information via About This Mac, and selecting the Installations item under Software.
Not that this update is likely to be installed after you have installed the 10.14.1, High Sierra, or Sierra Security Update – it is not included as part of those updates, but installed separately.
A full listing of security data file versions is given by LockRattler and SystHist for El Capitan, Sierra, High Sierra and Mojave, available from Downloads above. If your Mac has not yet installed this update, you can force an update using LockRattler, or at the command line.
I have updated the reference pages here which are accessed directly from LockRattler 4.2 and later using its Check blog button.