hide progress bar of curl

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   823  100   823    0     0   803k      0 --:--:-- --:--:-- --:--:--  803k

Author: vangie

nginx.conf

@@ -177,7 +177,7 @@ Environment="HTTPS_PROXY=$scheme://$http_host/"
 EOD
 
 # Get the CA certificate from the proxy and make it a trusted root.
-curl $scheme://$http_host/ca.crt > /usr/share/ca-certificates/docker_registry_proxy.crt
+curl -sS $scheme://$http_host/ca.crt > /usr/share/ca-certificates/docker_registry_proxy.crt
 if fgrep -q "docker_registry_proxy.crt" /etc/ca-certificates.conf ; then
    echo "certificate refreshed"
 else