[kovidgoyal]

Here is the set of steps to have calibre auto-update metadata-sources-cache.json

1. Restart calibre
2. Start a metadata download, it will probably still fail
3. Wait a minute or two for the cache to be updated
4. Restart calibre again
5. Now it should work

And if for any reason this fails to update metadata-sources-cache.json you can always delete it manually to restore functioning. To delete it manually, do the following:

1. Click Preferences->Miscellaneous
2. Click "Open calibre configuration directory"
3. Delete the file "metadata-sources-cache.json"
4. Restart calibre