message: pretty-print our in-repo json
  This is a first step toward highly diffable & mergeable storage.
diff: @@ -193,7 +193,7 @@ async function finalizer(pendingChange) {
  file.setContent(JSON.stringify({
  attributes: pendingChange.finalDocument.attributes,
  relationships: pendingChange.finalDocument.relationships
  - }));
  + }, null, 2));
  } else {
  file.delete();
  }
  