Typographical Errors

[evandrix]

• https://github.com/socialpoint-labs/sheetfu/blob/master/documentation/usage.rst#get_max_row
  get_max_row get_max_rows

• https://github.com/socialpoint-labs/sheetfu/blob/master/documentation/usage.rst#get_max_column
  get_max_column get_max_columns