plugins.vk: use html_unescape for HLS streams
plugins.vk: use html_unescape for HLS streams

Example Livestreams can be found on https://vk.com/video

```
$ streamlink https://vk.com/video-45085246_456239928 -l info
[cli][info] Found matching plugin vk for URL https://vk.com/video-45085246_456239928
[cli][info] Available streams: 360p (worst), 480p, 720p, 1080p (best)
[cli][info] Opening stream: 1080p (hls)
```

melmorabity/streamlink,chhe/streamlink,gravyboat/streamlink,gravyboat/streamlink,streamlink/streamlink,wlerin/streamlink,chhe/streamlink,bastimeyer/streamlink,melmorabity/streamlink,beardypig/streamlink,streamlink/streamlink,bastimeyer/streamlink,wlerin/streamlink,beardypig/streamlink