fix default cert path

Author: facundoolano

conf/sys.config

@@ -1,8 +1,8 @@
 [{webrtc_server, [
                   {port, 8443},
                   {hostname, <<"localhost">>},
-                  {certfile, <<"../../lib/webrtc_server/priv/certs/certificate.pem">>},
-                  {keyfile, <<"../../lib/webrtc_server/priv/certs/key.pem">>},
+                  {certfile, <<"priv/certs/certificate.pem">>},
+                  {keyfile, <<"priv/certs/key.pem">>},
                   {auth_fun, {example, authenticate}},
                   {create_callback, {example, create}},
                   {join_callback, {example, join}},