Given the parameters day, month and year, return whether that date is a valid date.
is_valid_date(35, 2, 2020) ➞ false
# February doesn't have 35 days.
is_valid_date(8, 3, 2020) ➞ true
# 8th March 2020 is a real date.
is_valid_date(31, 6, 1980) ➞ false
# June only has 30 days.N/A