message: allow backup to run as shell instead of bash
diff: -#!/bin/bash
  +#!/bin/sh
  set -eu -o pipefail
  @@ -46,7 +46,7 @@ function echo_status(){
  function backup_database(){
  backup_file="$BACKUP_DIR/$TIMESTAMP.$database.sql.gz"
  - output+="$database => $backup_file\n"
  + output="${output}${database} => $backup_file\n"
  echo_status "...backing up $count of $total databases: $database"
  $(pg_dump $database | gzip -9 > $backup_file)
  }
  