Move dokku-installer start to postinst

Performing the start in preinst meant that the required dokku-installer.rb file was not yet in position.

debian/postinst

@@ -13,6 +13,10 @@ case "$1" in
     egrep -i "^docker" /etc/group || groupadd docker
     usermod -aG docker dokku
     dokku plugins-install
+
+    if [ -f /etc/init/dokku-installer.conf ] && service dokku-installer status 2> /dev/null | grep waiting; then
+        sudo service dokku-installer start
+    fi
     ;;
 
   *)

debian/preinst

@@ -23,9 +23,6 @@ case "$1" in
 
     rm -f /etc/nginx/sites-enabled/*
     service nginx reload
-    if service dokku-installer status 2> /dev/null | grep waiting; then
-        sudo service dokku-installer start
-    fi
     ;;
 
   abort-upgrade)