message: pretty print meta.json
diff: @@ -77,7 +77,7 @@ pub fn save_metas(segment_metas: Vec<SegmentMeta>,
  schema: schema,
  opstamp: opstamp,
  };
  - let mut w = try!(serde_json::to_vec(&metas));
  + let mut w = try!(serde_json::to_vec_pretty(&metas));
  try!(write!(&mut w, "\n"));
  let res = directory.atomic_write(&META_FILEPATH, &w[..])?;
  debug!("Saved metas {:?}", serde_json::to_string_pretty(&metas));
  