The downloader doesn't seem to follow redirects, and instead get:
```
% curl https://nlp.stanford.edu/data/coqa/coqa-dev-v1.0.json
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>301 Moved Permanently</title>
</head><body>
<h1>Moved Permanently</h1>
<p>The document has moved <a href="https://downloads.cs.stanford.edu/nlp/data/coqa/coqa-dev-v1.0.json">here</a>.</p>
<hr>
<address>Apache/2.2.15 (CentOS) Server at nlp.stanford.edu Port 443</address>
</body></html>
```