Create a function that takes in an array and returns an array of the accumulating sum.
accumulatingArray([1, 2, 3, 4]) ➞ [1, 3, 6, 10]
// [1, 3, 6, 10] can be written as [1, 1 + 2, 1 + 2 + 3, 1 + 2 + 3 + 4]
accumulatingArray([1, 5, 7]) ➞ [1, 6, 13]
accumulatingArray([1, 0, 1, 0, 1]) ➞ [1, 1, 2, 2, 3]
accumulatingArray([]) ➞ []
An empty array input should return an empty array [].