input: Write a python function to compute the running total of an array using NumPy.
  assert np.array_equal(runningTotal([1, 2, 3, 4]), np.array([1, 3, 6, 10]))
  assert np.array_equal(runningTotal([0, 0, 0, 0]), np.array([0, 0, 0, 0]))
  assert np.array_equal(runningTotal([-1, -2, -3, -4]), np.array([-1, -3, -6, -10]))
  assert np.array_equal(runningTotal([5, 10, 15, 20]), np.array([5, 15, 30, 50]))
output: import numpy as np
  
  def runningTotal(arr):
      return np.cumsum(arr)