do not output message when creating ENV file

This fixes a bug introduced when deploying apps where the
nginx-vhosts plugin runs ``dokku config:get $APP NO_VHOST``. The initial
run of this actually was creating the ``ENV`` file and dumping to
stdout the value "NO_VHOST=-----> Creating /home/dokku/foo/ENV". This
was obviously no good because nginx-vhosts was considering this to be a
value of true.

I've modified this to simply not return anything when the value does not
exist. A better update may be to output the messages to stderr instead
of stdout.

plugins/config/commands

@@ -5,7 +5,6 @@ ENV_FILE="$DOKKU_ROOT/$2/ENV"
 ENV_FILE_TEMP="$DOKKU_ROOT/$2/ENV.tmp"
 config_create () {
   [ -f $ENV_FILE ] || {
-    echo "-----> Creating $ENV_FILE"
     touch $ENV_FILE
   }
 }