input: Write a function to return an array with the running total of numbers in a given list using numpy. If the given array is empty then return an empty array.
  
  import numpy as np
  
  def runningTotal(arr):
      return np.cumsum(arr)
  assert np.array_equal(runningTotal([1, 2, 3, 4]), np.array([1, 3, 6, 10]))
  assert np.array_equal(runningTotal([5, -1, 3, 7]), np.array([5, 4, 7, 14]))
  assert np.array_equal(runningTotal([]), np.array([]))
  assert np.array_equal(runningTotal([-1, -2, -3, -4]), np.array([-1, -3, -6, -10]))
output: import numpy as np
  
  def runningTotal(arr):
      return np.cumsum(arr)