Given a string of letters, how many capital letters are there?
capital_letters("fvLzpxmgXSDrobbgMVrc") ➞ 6 capital_letters("JMZWCneOTFLWYwBWxyFw") ➞ 14 capital_letters("mqeytbbjwqemcdrdsyvq") ➞ 0
N/A