Add update_task to proglearn for data streaming

[KevinWang905]

Part of #34: Add a function that updates previous tasks based on new data with task labels

[nhahn7]

@PSSF23 Can you assign me to this issue? Thanks

[PSSF23]

@nhahn7 I also save the test here in case the test file is changed in the future.

def test_update_task(self):
   np.random.seed(1)

   l2f = LifelongClassificationForest()

   X = np.concatenate((np.zeros(100), np.ones(100))).reshape(-1, 1)
   y = np.concatenate((np.zeros(100), np.ones(100)))

   l2f.add_task(X, y)
   u1 = l2f.predict_proba(np.array([0]).reshape(1, -1), task_id=0)
   u2 = l2f.predict_proba(np.array([1]).reshape(1, -1), task_id=0)

   X2 = np.concatenate((np.zeros(100), np.ones(100))).reshape(-1, 1)
   y2 = np.concatenate((np.zeros(100), np.ones(100)))

   X3 = np.concatenate((X, X2))
   y3 = np.concatenate((y, y2))

   l2f.update_task(X2, y2, task_id=0)

  assert np.array_equiv(l2f.task_id_to_X[0], X3)
   assert np.array_equiv(l2f.task_id_to_y[0], y3)