Create a function that takes a string and returns true if the sum of the position of every letter in the alphabet is even and false if the sum is odd.
is_alpha("i'am king") ➞ true
# 9 + 1 + 13 + 11 + 9 + 14 + 7 = 64 (even)
is_alpha("True") ➞ true
# 20 + 18 + 21 + 5= 64 (even)
is_alpha("alexa") ➞ false
# 1 + 12 + 5 + 24 + 1= 43 (odd)