Stuff installed by the third party section of the software center doesn't get updated automatically along with system updates.
You need to update it manually. To do that, you can go to the third party section and install it again (it will pull in the latest version available).
You can also do this via the command line (in my experience, doing it this way is faster).
First run this command:
sudo eopkg bi --ignore-safety https://raw.githubusercontent.com/getsolus/3rd-party/master/network/web/browser/google-chrome-stable/pspec.xml
and run this one after the first command completes:
sudo eopkg it google-chrome-*.eopkg;sudo rm google-chrome-*.eopkg
source: Help Center