text: Title: Latest requirements.txt seems to be over-specifying dependencies
  Body: This is the latest version requirements.txt file:
  
  ```
  black>=19.3b0
  darglint
  hypothesis>=4.4.0
  interrogate
  ipykernel
  isort>=4.3.18
  jupyter_client
  lxml
  natsort
  nbsphinx>=0.4.2
  pandas-flavor
  pandas-vet
  pre-commit
  pyspark
  pytest-azurepipelines
  pytest-cov
  pytest>=3.4.2
  scikit-learn
  seaborn
  setuptools>=38.5.2
  sphinxcontrib-fulltoc==1.2.0
  unyt
  xarray
  ```
  
  Those are inject in the setup.py as mandatory dependencies but a lot in there looks like docs, dev, or optional. Is pyjanitor really require all that at run time?