Fix captions not supporting links. (#6422)
Fix captions not supporting links. (#6422)

What's changed, or what was fixed?

We ran into an issue with video captions not supporting inline links. As this is live, I'm going to drop the link while I try to play around with what can render.

![image](https://user-images.githubusercontent.com/110953/43151644-4629a406-8f21-11e8-99b9-4b21b257605e.png)


- [ ] This has been reviewed and approved by (NAME)
- [x] I have run `npm test` locally and all tests pass.
- [x] I have added the appropriate `type-something` label.
- [x] I've staged the site and manually verified that my content displays correctly.

**CC:** @petele

myakura/WebFundamentals,sonyarianto/WebFundamentals,google/WebFundamentals,samdutton/WebFundamentals,samdutton/WebFundamentals,agektmr/WebFundamentals,lucab85/WebFundamentals,lucab85/WebFundamentals,sonyarianto/WebFundamentals,google/WebFundamentals,agektmr/WebFundamentals,samdutton/WebFundamentals,samdutton/WebFundamentals,google/WebFundamentals,google/WebFundamentals,agektmr/WebFundamentals,myakura/WebFundamentals,sonyarianto/WebFundamentals,agektmr/WebFundamentals,lucab85/WebFundamentals,lucab85/WebFundamentals,myakura/WebFundamentals,sonyarianto/WebFundamentals,myakura/WebFundamentals