rpcclient: Explicitly require TLS >= 1.2 for HTTP.

This set the TLS config to explicitly require TLS 1.2 as the minimum
version for HTTP connections to explicitly match the requirement it
imposes for WebSocket connections.

This is technically a noop for the more recent Go releases that are
officially supported since TLS 1.2 is the default minimum when acting as
a client for those releases, however, it is preferable to be explicit
and consistent.

rpcclient/infrastructure.go

@@ -1187,7 +1187,8 @@ func newHTTPClient(config *ConnConfig) (*http.Client, error) {
 			pool := x509.NewCertPool()
 			pool.AppendCertsFromPEM(config.Certificates)
 			tlsConfig = &tls.Config{
-				RootCAs: pool,
+				RootCAs:    pool,
+				MinVersion: tls.VersionTLS12,
 			}
 		}
 	}