This entry from Security Metrics shows that they are able to see your SSL certificate. This could be a publicly signed cert or a self-signed cert.
Visibility of the public key of the certificate is required for SSL communication. Not a security risk or vulnerability.
Being able to see the public key of your certificate is required for SSL communication. That is the point of SSL and part of the protocol negotiation. Seeing this cert is not a risk nor a vulnerability.
No action required.