Fix link to swin transformers v2 microsoft model
# What does this PR do?

The link `https://huggingface.co/microsoft/swinv2_tiny_patch4_windows8_256/` redirects to a 404. The actual link is https://huggingface.co/microsoft/swinv2-tiny-patch4-window8-256.

At the same time, loading the configuration using 
```python3
from transformers import AutoConfig
config = AutoConfig.from_pretrained("microsoft/swinv2_tiny_patch4_windows8_256")
```
Returns 
```
HTTPError: 401 Client Error: Unauthorized for url: 
https://huggingface.co/microsoft/swinv2_tiny_patch4_windows8_256/resolve/main/config.json
```

As the link is not valid, this change fixes it.
_The documentation is not available anymore as the PR was closed or merged._