message: Update http body impl in h2 example
diff: @@ -37,14 +37,14 @@ impl RspBody {
  }
  impl Body for RspBody {
  - type Item = <Bytes as IntoBuf>::Buf;
  + type Data = <Bytes as IntoBuf>::Buf;
  type Error = h2::Error;
  fn is_end_stream(&self) -> bool {
  self.0.as_ref().map(|b| b.is_empty()).unwrap_or(false)
  }
  - fn poll_buf(&mut self) -> Poll<Option<Self::Item>, h2::Error> {
  + fn poll_data(&mut self) -> Poll<Option<Self::Data>, h2::Error> {
  let data = self.0.take().and_then(|b| {
  if b.is_empty() {
  None
  