Let's encrypt certificate

Hello there. I am using https Grafana with “Let’s encrypt” certificate https://sensors.issgreppi.it
It work fine with Firefox, but with google I had “ERR_CERT_AUTHORITY_INVALID”.
I googled and found examples with Apache/IIS/… about “chained” certificate or bundle certificate (I have this file), but: how to add in Grafana.ini?

May config (work with firefox):
protocol = https
cert_file = /etc/grafana/certificate.crt
cert_key = /etc/grafana/private.key