cant install composer says certificate issue

I am trying to install composer

sudo curl -sS https://getcomposer.org/installer | sudo php

But its says : curl: (60) Peer's Certificate issuer is not recognized. If you'd like to turn off curl's verification of the certificate, use the -k (or --insecure) option.

So i tried this :

sudo curl  -k -sS https://getcomposer.org/installer | sudo php

But still its not working.