change SSL certificate fingerprint whitelisting from SHA1 to SHA-256

SHA1 is too close to bruteforceable

contrib/epee/include/net/net_ssl.h

@@ -37,6 +37,8 @@
 #include <boost/asio/ssl.hpp>
 #include <boost/system/error_code.hpp>
 
+#define SSL_FINGERPRINT_SIZE 32
+
 namespace epee
 {
 namespace net_utils