[atlas] SSL issue with atlas.ripe.net

Hello,

I'm facing an issue while using Atlas API.

Some connections (not all) to https://atlas.ripe.net fail because of
what seems to be an invalid certs chain. It looks like that an
intermediate cert is missing.

SSLLabs too reports something similar:
https://www.ssllabs.com/ssltest/analyze.html?d=atlas.ripe.net&s=193.0.6.158

$ openssl s_client -connect atlas.ripe.net:443 -servername atlas.ripe.net
CONNECTED(00000003)
depth=0 C = NL, ST = Noord-Holland, L = Amsterdam, O = RIPE NCC, CN =
atlas.ripe.net
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 C = NL, ST = Noord-Holland, L = Amsterdam, O = RIPE NCC, CN =
atlas.ripe.net
verify error:num=27:certificate not trusted
verify return:1
depth=0 C = NL, ST = Noord-Holland, L = Amsterdam, O = RIPE NCC, CN =
atlas.ripe.net
verify error:num=21:unable to verify the first certificate
verify return:1
---
Certificate chain
 0 s:/C=NL/ST=Noord-Holland/L=Amsterdam/O=RIPE NCC/CN=atlas.ripe.net
   i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High
Assurance Server CA
---
Server certificate
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
subject=/C=NL/ST=Noord-Holland/L=Amsterdam/O=RIPE NCC/CN=atlas.ripe.net
issuer=/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High
Assurance Server CA
---
...
    Verify return code: 21 (unable to verify the first certificate)


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