Use printf instead of echo like docker docs do

abra

@@ -665,7 +665,7 @@ sub_app_secret_insert() {
     error "Required arguments missing"
   fi
 
-  echo "$PW" | docker secret create "${STACK_NAME}_${SECRET}_${VERSION}" - > /dev/null
+  printf "$PW" | docker secret create "${STACK_NAME}_${SECRET}_${VERSION}" - > /dev/null
 
   if [ "$STORE_WITH_PASS" == "true" ] && type pass > /dev/null 2>&1; then
     echo "$PW" | pass insert "hosts/$DOCKER_CONTEXT/${STACK_NAME}/${SECRET}" -m > /dev/null