JSON LD schema.org metadata invalid on pages that integrate the client

# Description

Google Search Console detected the following error

[Unparsable structured data](https://search.google.com/search-console/r/unknown-type?resource_id=https%3A%2F%2Felifesciences.org%2F)

Parsing error: Missing ',' or '}'

# 2 articles are impacted:

https://elifesciences.org/articles/16415
https://elifesciences.org/articles/13764

**16415:**

```
},
"headline": "Ancient origin of lubricated joints in bony vertebrates",
"datePublished": "2016-07-19",
"author": [
```

**13664:**
```
"headline": "Distinct roles of visual, parietal, and frontal motor cortices in memory-guided sensorimotor decisions",
"datePublished": "2016-08-04",
"author": [
```

I suspect that something in the hypothesis client code is creating this bug. For our purpose we strip tags out of the headline value but you will certainly want to escape the string.