Fix some bugs in setup for stack flavor

- Unbound and webmail images were hardcoded
- Removed unnecesary environment keyword

setup/flavors/stack/docker-compose.yml

@@ -33,7 +33,7 @@ services:
 
   {% if resolver_enabled %}
   resolver:
-    image: mailu/unbound:{{ version }}
+    image: ${DOCKER_ORG:-mailu}/unbound:${MAILU_VERSION:-{{ version }}}
     env_file: {{ env }}
     networks:
       default:
@@ -56,7 +56,6 @@ services:
   imap:
     image: ${DOCKER_ORG:-mailu}/dovecot:${MAILU_VERSION:-{{ version }}}
     env_file: {{ env }}
-    environment:
     volumes:
       - "{{ root }}/mail:/mail"
       - "{{ root }}/overrides:/overrides"
@@ -130,7 +129,7 @@ services:
 
   {% if webmail_type != 'none' %}
   webmail:
-    image: ${DOCKER_ORG:-mailu}/roundcube:${MAILU_VERSION:-{{ version }}}
+    image: ${DOCKER_ORG:-mailu}/{{ webmail_type }}:${MAILU_VERSION:-{{ version }}}
     env_file: {{ env }}
     volumes:
       - "{{ root }}/webmail:/data"