[RC] Bump to 1.6

+ Fix broken plugin installation by updating composer option

roundcube/Dockerfile

@@ -1,4 +1,4 @@
-FROM roundcube/roundcubemail:1.4.12-apache
+FROM roundcube/roundcubemail:1.6.0-apache
 
 RUN a2enmod remoteip; \
     echo "RemoteIPHeader X-Forwarded-For" > /etc/apache2/conf-available/remoteip.conf; \
@@ -20,7 +20,7 @@ RUN set -ex; \
     composer \
         --working-dir=/usr/src/roundcubemail/ \
         --prefer-dist --prefer-stable \
-        --no-update --no-interaction \
+        --update-no-dev --no-interaction \
         --optimize-autoloader --apcu-autoloader \
         require \
             roundcube/carddav \

roundcube/docker-compose.yml

@@ -3,7 +3,7 @@ version: "3.8"
 services:
   app:
     build: .
-    image: my_roundcube:1.4.12
+    image: my_roundcube:1.6.0
     restart: unless-stopped
     depends_on:
       - db