README: update SSL script to generate sha256 cert

README.md

@@ -131,7 +131,7 @@ openssl req -new -x509 -days 365 -key ca.key -subj "/C=CN/ST=GD/L=SZ/O=Acme, Inc
 
 # server certificate (for multiple domains, change subjectAltName to: DNS:example.com,DNS:www.example.com)
 openssl req -newkey rsa:2048 -nodes -keyout server.key -subj "/C=CN/ST=GD/L=SZ/O=Acme, Inc./CN=localhost" -out server.csr
-openssl x509 -req -extfile <(printf "subjectAltName=DNS:localhost") -days 365 -in server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt
+openssl x509 -sha256 -req -extfile <(printf "subjectAltName=DNS:localhost") -days 365 -in server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt
 
 # client certificate (the p12/pem format may be useful for some clients)
 openssl req -newkey rsa:2048 -nodes -keyout client.key -subj "/C=CN/ST=GD/L=SZ/O=Acme, Inc./CN=client" -out client.csr