There is also a second, less invasive change you can try.
On line 485 (of 0.5.0) you will find this line:
nonce="$(http_request head "${CA}" | grep Replay-Nonce: | awk -F ': ' '{print $2}' | tr -d '\n\r')"
If you add a -i after the grep, like below:
nonce="$(http_request head "${CA}" | grep -i Replay-Nonce: | awk -F ': ' '{print $2}' | tr -d '\n\r')"
it should also fix your problem.
The underlying change that triggered this is probably the move to Cloudflare and HTTP/2 that happened today, where headers are canonicalized to lower case (at least, that’s the way curl outputs them).
But you should really upgrade to 0.6.5.