message: Implement pretty-printer case for JSXSpreadChild.
diff: @@ -1083,6 +1083,9 @@ function genericPrintNoParens(path, options, print) {
  case "JSXSpreadAttribute":
  return concat(["{...", path.call(print, "argument"), "}"]);
  + case "JSXSpreadChild":
  + return concat(["{...", path.call(print, "expression"), "}"]);
  +
  case "JSXExpressionContainer":
  return concat(["{", path.call(print, "expression"), "}"]);
  