a little bug in detection/demo.py/gen_cam()

```python
def gen_cam(image, mask):
    heatmap = cv2.applyColorMap(np.uint8(255 * mask), cv2.COLORMAP_JET)
    # heatmap = np.float32(heatmap) / 255  # little bug here
    heatmap = np.float32(heatmap)
    heatmap = heatmap[..., ::-1]  # gbr to rgb
    cam = heatmap + np.float32(image)
    return norm_image(cam), heatmap
```
For variable "heatmap" there is no need to divide by 255.