getLastMssg = async con_id => {
  let [{ last }] = await db.query(
    'SELECT MAX(message_id) AS last FROM messages WHERE con_id = ?',
    [con_id]
  )
  let l = await db.query(
    'SELECT message, type, mssg_by FROM messages WHERE message_id=?',
    [last]
  )
  return l[0]
}
Returns last message of a comversation
@param {Number} con_id Conversation ID