Replace .iteritems() with items() for python3 compatibility

postgrest/nginx.sls

-{% for instance_name, instance_conf in salt['pillar.get']("postgrest:instances").iteritems() %}
+{% for instance_name, instance_conf in salt['pillar.get']("postgrest:instances").items() %}
 {% if instance_conf.nginx is defined %}
 
 postgrest_{{ instance_name }}_nginx_conf:

postgrest/postgrest.sls

-{% for instance_name, instance_conf in salt['pillar.get']("postgrest:instances").iteritems() %}
+{% for instance_name, instance_conf in salt['pillar.get']("postgrest:instances").items() %}
 {% set tag = instance_conf.tag %}
 
 postgrest_{{ instance_name }}_fetch:

postgrest/tpl/postgrest.conf

 # This file is written by salt. Don't even think about it.
-{% for key, value in postgrest_conf.iteritems() %}{{ key }} = {% if value is string %}"{{ value }}"{% else %}{{ value }}{% endif %}
+{% for key, value in postgrest_conf.items() %}{{ key }} = {% if value is string %}"{{ value }}"{% else %}{{ value }}{% endif %}
 {% endfor %}