correct PinSAGE knn example syntax (#1617)

Co-authored-by: Quan (Andy) Gan <coin2028@hotmail.com>
Co-authored-by: Chao Ma <mctt90@gmail.com>

examples/pytorch/pinsage/README.md

@@ -25,7 +25,7 @@ interacted.  The distance between two items are measured by Euclidean distance o
 item embeddings, which are learned as outputs of PinSAGE.
 
 ```
-python model.py data.pkl --num-epochs 300 --num-workers 2 --device cuda:0 data.pkl --hidden-dims 64
+python model.py data.pkl --num-epochs 300 --num-workers 2 --device cuda:0 --hidden-dims 64
 ```
 
 The HITS@10 is 0.01241, compared to 0.01220 with SLIM with the same dimensionality.