rail-fence-cipher: improve stub file (#1263)
rail-fence-cipher: improve stub file (#1263)


exercism/xpython,exercism/python,N-Parsons/exercism-python,exercism/python,jmluy/xpython,smalley/python,smalley/python,behrtam/xpython,behrtam/xpython,N-Parsons/exercism-python,jmluy/xpython,exercism/xpython