fixed a bash scripting bug in start.sh that prevented horizon from ever starting

contrib/docker/start.sh

@@ -12,7 +12,7 @@ php artisan migrate --force
 php artisan update
 
 # Run a worker if it is set as embedded
-if [ $HORIZON_EMBED = true ]; then
+if [ "$HORIZON_EMBED" -eq "true" ]; then
 	php artisan horizon &
 fi