Correct javadoc for append operation

  /**
   * Appends values to one or more columns within a single row.
   * <p>
   * This operation guaranteed atomicity to readers. Appends are done
   * under a single row lock, so write operations to a row are synchronized, and
   * readers are guaranteed to see this operation fully completed.
   *
   * @param append object that specifies the columns and amounts to be used
   *                  for the increment operations
   * @throws IOException e
   * @return values of columns after the append operation (maybe null)
   */