input: Write a function to calculate the running total of numbers in a given list using numpy. If the given list 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]), [1, 3, 6, 10])
  assert np.array_equal(runningTotal([10, 20, 30]), [10, 30, 60])
  assert np.array_equal(runningTotal([-1, 1, -1, 1]), [-1, 0, -1, 0])
  assert np.array_equal(runningTotal([]), [])
output: import numpy as np
  
  def runningTotal(arr):
      if len(arr) == 0:
          return np.array([])
      return np.cumsum(arr)