Fix typo in luna16 detection tutorial (#1826)

### Checks
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- [ ] Avoid including large-size files in the PR.
- [ ] Clean up long text outputs from code cells in the notebook.
- [ ] For security purposes, please check the contents and remove any
sensitive info such as user names and private key.
- [ ] Ensure (1) hyperlinks and markdown anchors are working (2) use
relative paths for tutorial repo files (3) put figure and graphs in the
`./figure` folder
- [ ] Notebook runs automatically `./runner.sh -t <path to .ipynb file>`

Signed-off-by: YunLiu <[email protected]>

detection/generate_transforms.py

@@ -148,7 +148,7 @@ def generate_detection_train_transform(
                 spatial_axes=(0, 1),
             ),
             # apply the same affine matrix which already applied on the images to the points
-            ApplyTransformToPointsd(keys=[point_key], refer_key=image_key, affine_lps_to_ras=affine_lps_to_ras),
+            ApplyTransformToPointsd(keys=[point_key], refer_keys=image_key, affine_lps_to_ras=affine_lps_to_ras),
             # convert points back to boxes
             ConvertPointsToBoxesd(keys=[point_key]),
             ClipBoxToImaged(