JsonRequestSpec: stream with adhoc request filter 

https://travis-ci.com/github/playframework/play-ws/jobs/323723859
```
[info] JsonRequestSpec
[error]   x stream with adhoc request filter
[error]    Timeout after 25 seconds (retries = 0, timeout = 5 seconds), timeFactor = 5 (AhcWSRequestFilterSpec.scala:82)
```