When adding videos to a YouTube playlist, cache is not updated

### What Red version are you using?

3.4.16

### What were you trying to do?

I have added new videos in a YouTube playlist (which went fron 58 to 70 videos) then tried playing it through Red.

### What did you expect to happen?

Red would list/queue the total amount of videos listed in the playlist (70)

### What actually happened?

Red is listing/queueing the previous amount of videos listed in the playlist (58)

### How can we reproduce this error?

1. Create a new YouTube playlist, add an amount of videos
2. Play the playlist through Red so that it gets cached (-play http:\\youtubeplaylisturl)
3. Red should list/queue the correct amount of videos
4. (May need to wait a few days)
5. Add videos in the playlist
6. Play the playlist again through Red using the same previous command
7. Red should list the previous amount of videos, and not queue the new videos added.

### Anything else?

I have not found a command or a way to clear the cache? The only workaround we found so far is to disable the cache.

Maybe the cache should be checked to know if it's still up to date, when a cached link is called? I mean, it goes against the concept of cache, but in the case of playlists, there's otherwise no way to know if the playlist was updated since last cached.