Update tasks.py

[zeref02]

  def get_overdue(loan_period):
  # check for overdue articles
  today = nowdate()

overdue_by_member = {}
articles_transacted = []

for d in frappe.db.sql("""select name, article, article_name, library_member, member_name
    from `tabLibrary Transaction` order by transaction_date desc, modified desc""", as_dict=1):

    if d.article in articles_transacted:
        continue

    if d.transaction_type=="Issue" and date_diff(today, d.transaction_date) > loan_period:
        overdue_by_member.setdefault(d.library_member, [])
        overdue_by_member[d.library_member].append(d)

    articles_transacted.append(d.article)

In the given code query didn't include the "transaction_date" too. I missed that in the previous pull request.