Prefer to return any transcript format except text/*, if other formats are available

[mitchdowney]

See the Podnews Weekly Review RSS feed for an example. They offer multiple transcript formats. The "text/html" one is a more simplified version, while the application/json version has better timestamp support. When multiple transcript formats are available, we should not use text/html.

https://feeds.buzzsprout.com/1538779.rss