For now you can choose to ignore it or trash it since caches can always be removed without causing any issues. The signature was just added by the Cisco/ClamAV folks today.
You are correct that it addresses a vulnerability in Microsoft Edge that was patched yesterday, so of no concern to macOS/OS X users who are not also running Windows on their Mac. With what we know about Yahoo hacking it could easily be a correctly identified exploit attempt.
Another user has already opened a ticket with the ClamXav Help Desk on this, so there may be additional information available tomorrow.
21.5" iMac Quad-core i7 / Mac OS X 10.9.5, 10.10.5 & 10.11.6 / ClamXav 2.12.1 (ClamAV® 0.99.2)