SSL/TLS letsencrypt unknown CA #848

Environment

VerneMQ Version: 1.5.0

OS: Ubuntu 18.04.1 LTS

Erlang/OTP version (if building from source):

Expected behavior

I have added the certificate files to vernemq.conf

listener.ssl.cafile = /etc/vernemq/chain.pem
listener.ssl.keyfile = /etc/vernemq/privkey.pem
listener.ssl.certfile = /etc/vernemq/cert.pem

I have copied the files from letsencrypt into vernemq folder and chowned the files with :
chown vernemq:vernemq *.pem in order for vernemq to read the files.

listener.ssl.default = 0.0.0.0:8883
listener.tcp.default = 0.0.0.0:1883

The unencrypted version works as expected, and I expect that the ssl-listener should work with :

mosquitto_pub -h domain.com -t test -m "hello" -p 8883 --capath /etc/ssl/certs -u "xxx" -P "yyy"

Actual behaviour

mosquitto_pub prints: Error: A TLS error occurred.
vernemq prints: SSL: certify: ssl_alert.erl:88:Fatal error: unknown ca in the logs.