Make version PEP 440 compliant

[JanNash]

pip complained:

(tapeit) jannash TapeIt $ python --version
Python 3.8.10
(tapeit) jannash TapeIt $ pip install -r requirements.txt
Collecting xunique
  Cloning https://github.com/Tonband/xunique (to revision v4.1.7-Tonband) to /private/var/folders/r1/nxkw72xs1hqfxwj_t3x7s99w0000gn/T/pip-install-ov1vuiat/xunique_31a6466b675f4339af1b442d7de0dd5c
  Running command git clone -q https://github.com/Tonband/xunique /private/var/folders/r1/nxkw72xs1hqfxwj_t3x7s99w0000gn/T/pip-install-ov1vuiat/xunique_31a6466b675f4339af1b442d7de0dd5c
  Running command git checkout -q 45e5a066373b1670006da2a022b75cf135e1b323
Collecting natsort>=7.1
  Using cached natsort-7.1.1-py3-none-any.whl (35 kB)
Building wheels for collected packages: xunique
  Building wheel for xunique (setup.py) ... done
  Created wheel for xunique: filename=xUnique-4.1.7_Tonband-py3-none-any.whl size=13293 sha256=3ec78483bad12e9c35fbd03599197cbeb7c621ffa87c20908b5e9b1954259bda
  Stored in directory: /private/var/folders/r1/nxkw72xs1hqfxwj_t3x7s99w0000gn/T/pip-ephem-wheel-cache-43reb13o/wheels/02/f4/2c/3129a225022374bb6868fb3d15d9034c04c41ee8a240061e84
  WARNING: Built wheel for xunique is invalid: Metadata 1.2 mandates PEP 440 version, but '4.1.7-Tonband' is not
Failed to build xunique
Installing collected packages: natsort, xunique
    Running setup.py install for xunique ... done
  DEPRECATION: xunique was installed using the legacy 'setup.py install' method, because a wheel could not be built for it. A possible replacement is to fix the wheel build issue reported above. You can find discussion regarding this at https://github.com/pypa/pip/issues/8368.
Successfully installed natsort-7.1.1 xunique-4.1.7-Tonband
(tapeit) jannash TapeIt $