Use cmd with runas parameter

Replace the deprecated user and group parameters with runas to fix
deprecation warnings.

states/webserver/init.sls

@@ -18,8 +18,7 @@ generate-dhparam-nginx:
   cmd.run:
     - name: openssl dhparam -out {{ ssldir }}/dhparams.pem 2048
     - umask: 022
-    - user: root
-    - group: root
+    - runas: root
     - creates: {{ ssldir }}/dhparams.pem
     - require_in:
       - file: /etc/nginx/conf.d/ssl.conf