modify python3 to python in .sh

fluid/PaddleCV/video/scripts/infer/infer_nextvlad.sh

-python3 infer.py --model-name="NEXTVLAD" --config=./configs/nextvlad.txt --filelist=./data/youtube8m/infer.list \
+python infer.py --model-name="NEXTVLAD" --config=./configs/nextvlad.txt --filelist=./data/youtube8m/infer.list \
                 --weights=./checkpoints/NEXTVLAD_epoch0 \
                 --save-dir="./save"

fluid/PaddleCV/video/scripts/infer/infer_stnet.sh

-python3 infer.py --model-name="STNET" --config=./configs/stnet.txt --filelist=./data/kinetics/infer.list \
+python infer.py --model-name="STNET" --config=./configs/stnet.txt --filelist=./data/kinetics/infer.list \
                 --log-interval=10 --weights=./checkpoints/STNET_epoch0 --save-dir=./save

fluid/PaddleCV/video/scripts/infer/infer_tsn.sh

-python3 infer.py --model-name="TSN" --config=./configs/tsn.txt --filelist=./data/kinetics/infer.list \
+python infer.py --model-name="TSN" --config=./configs/tsn.txt --filelist=./data/kinetics/infer.list \
                 --log-interval=10 --weights=./checkpoints/TSN_epoch0 --save-dir=./save

fluid/PaddleCV/video/scripts/test/test_stnet.sh

-python3 test.py --model-name="STNET" --config=./configs/stnet.txt \
+python test.py --model-name="STNET" --config=./configs/stnet.txt \
                 --log-interval=10 --weights=./checkpoints/STNET_epoch0

fluid/PaddleCV/video/scripts/test/test_tsn.sh

-python3 test.py --model-name="TSN" --config=./configs/tsn.txt \
+python test.py --model-name="TSN" --config=./configs/tsn.txt \
                 --log-interval=10 --weights=./checkpoints/TSN_epoch0

fluid/PaddleCV/video/scripts/train/train_stnet.sh

-python3 train.py --model-name="STNET" --config=./configs/stnet.txt --epoch-num=60 \
+python train.py --model-name="STNET" --config=./configs/stnet.txt --epoch-num=60 \
                 --valid-interval=1 --save-interval=1 --log-interval=10

fluid/PaddleCV/video/scripts/train/train_tsn.sh

-python3 train.py --model-name="TSN" --config=./configs/tsn.txt --epoch-num=45 \
+python train.py --model-name="TSN" --config=./configs/tsn.txt --epoch-num=45 \
                 --valid-interval=1 --save-interval=1 --log-interval=10