Log Message:
Update to http2-3.0.3

3.0.3
* Return correct status messages in HTTP2 client
  (#31)[https://github.com/kazu-yamamoto/http2/pull/31]
* Follow changes in Aeson 2
  (#32)[https://github.com/kazu-yamamoto/http2/pull/32]
* Make sure connection preface is always sent first
  (#33)[https://github.com/kazu-yamamoto/http2/pull/33]
* Avoid empty data (#34)[https://github.com/kazu-yamamoto/http2/pull/34]

3.0.2
* Skip inserting entries that do not fit in the encoding table
  (#28)[https://github.com/kazu-yamamoto/http2/pull/28]