Update vehicleplate_postprocess.py

[hzhmybatis]

修复车牌识别执行报错 AttributeError: module 'numpy' has no attribute 'int'. [np.int](http://np.int/) was a deprecated alias for the builtin int. To avoid this error in existing code, use int by itself. Doing this will not modify any behavior and is safe. When replacing [np.int](http://np.int/), you may wish to use e.g. np.int64 or np.int32 to specify the precision. If you wish to review your current use, check the release note link for additional information.

[paddle-bot[bot]]

Thanks for your contribution!

[CLAassistant]

All committers have signed the CLA.

[paddle-bot[bot]]

Automatically closed by Paddle-bot.