Revert "Remove merge argument from pillar.get"

This reverts commit f6ba9ddb59.

the nginx.ng formula is only compatible with the upcoming feature
release, as noted here:

https://github.com/saltstack-formulas/nginx-formula#nginxng

nginx/ng/map.jinja

@@ -70,7 +70,7 @@
         },
         'managed': {},
     },
-}) %}
+}, merge=True) %}
 
 {% if 'user' not in nginx.server.config %}
 {% do nginx.server.config.update({