Inswapper model is missing

the [inswapper example](https://github.com/deepinsight/insightface/blob/master/examples/in_swapper/inswapper_main.py) doesn't work because of the missing model.

codes to reproduce the issue with insightface v0.7.3.

```
>>> import insightface
>>> swapper = insightface.model_zoo.get_model('inswapper_128.onnx', download=True, download_zip=True)
download_path: /Users/daishuo/.insightface/models/inswapper_128.onnx
Downloading /Users/daishuo/.insightface/models/inswapper_128.onnx.zip from https://github.com/deepinsight/insightface/releases/download/v0.7/inswapper_128.onnx.zip...
Traceback (most recent call last):
File "", line 1, in
File "/opt/anaconda3/envs/dev/lib/python3.7/site-packages/insightface/model_zoo/model_zoo.py", line 90, in get_model
model_file = download_onnx('models', model_file, root=root, download_zip=download_zip)
File "/opt/anaconda3/envs/dev/lib/python3.7/site-packages/insightface/utils/storage.py", line 49, in download_onnx
overwrite=True)
File "/opt/anaconda3/envs/dev/lib/python3.7/site-packages/insightface/utils/download.py", line 73, in download_file
raise RuntimeError("Failed downloading url %s" % url)
RuntimeError: Failed downloading url https://github.com/deepinsight/insightface/releases/download/v0.7/inswapper_128.onnx.zip
```