old_contents: from setuptools import find_packages, setup
  
  setup(
      name="regcore",
      version="3.1.0",
      license="public domain",
      packages=find_packages(),
      include_package_data=True,
      install_requires=[
          'cached_property',
          'django>=1.8,<1.12',
          'django-mptt',
          'jsonschema',
          'six',
          'webargs',
      ],
      extras_require={
          'backend-elastic': ['pyelasticsearch'],
          'backend-haystack': ['django-haystack'],
          'backend-pgsql': ['django>=1.10', 'psycopg2'],
      },
  )
  
new_contents: from setuptools import find_packages, setup
  
  setup(
      name="regcore",
      version="4.0.0",
      license="public domain",
      packages=find_packages(),
      include_package_data=True,
      install_requires=[
          'cached_property',
          'django>=1.8,<1.12',
          'django-mptt',
          'jsonschema',
          'six',
          'webargs',
      ],
      extras_require={
          'backend-elastic': ['pyelasticsearch'],
          'backend-haystack': ['django-haystack'],
          'backend-pgsql': ['django>=1.10', 'psycopg2'],
      },
  )
  
subject: Bump version to 4.0.0.