Create a function that takes a string and censors words over four characters with *.
censor("The code is fourty") ➞ "The code is ******"
censor("Two plus three is five") ➞ "Two plus ***** is five"
censor("aaaa aaaaa 1234 12345") ➞ "aaaa ***** 1234 *****"
* is the same as the length of the word.