Timing out `jq` execution.

Heroku has been timing out like this:

```
Jul 30 08:24:47 jqplay heroku/router: at=error code=H12 desc="Request timeout"
method=POST path="/jq" host=jqplay.org
request_id=4b1a93f0-69f8-412e-a19e-b10dfed3b7f6 fwd="193.41.234.229"
dyno=web.1 connect=1ms service=30876ms status=503 bytes=0
```