fix examples/demo.ipynb

[ywangmy]

change

fig = plt.figure(figsize=(10, 5))
for i, pred in enumerate(preds):
    plt.subplot(1, 2, i + 1)
    plt.imshow(frames[1])
    plt.title(f'frame[{i}]')
    for detection in pred:
        plt.scatter(detection[:,0], detection[:,1], 2)

to

fig = plt.figure(figsize=(10, 5))
for i, detection in enumerate(preds):
    plt.subplot(1, 2, i + 1)
    plt.imshow(frames[1])
    plt.title(f'frame[{i}]')
    plt.scatter(detection[:,0], detection[:,1], 2)