Create a function that takes a 2D array arr and returns the sum of the minimum value in each row.
sum_minimums([
[1, 2, 3, 4, 5],
[5, 6, 7, 8, 9],
[20, 21, 34, 56, 100]
]) ➞ 26
# minimum value of the first row is 1
# minimum value of the second row is 5
# minimum value of the third row is 20N/A