Forces the domain to be lowercase

[heuri]

Fixes problems with non lower case SNI requests - e.g. https://LuA-ReStY-AuTo-SsL.TlD

Solves this error:

issue_cert(): auto-ssl: issuing new certificate failed: dehydrated succeeded, but no certs present
auto-ssl: could not get certificate for LuA-ReStY-AuTo-SsL.TlD - using fallback - failed to get or issue certificate

Reproduce:

curl -i https://LuA-ReStY-AuTo-SsL.TlD