input: Write a function to return an array with the running total of numbers in a given list using numpy.
  
  ### Input:
  import numpy as np
  
  def runningTotal(arr):
      return np.cumsum(arr)
  
  ### Output:
  assert np.array_equal(runningTotal([1, 2, 3, 4]), [1, 3, 6, 10])
  assert np.array_equal(runningTotal([5, 6, 7, 8]), [5, 11, 18, 26])
  assert np.array_equal(runningTotal([10, -5, 15, -20]), [10, 5, 20, 0])
  assert np.array_equal(runningTotal([]), [])
output: import numpy as np
  
  def runningTotal(arr):
      return np.cumsum(arr)