text: Title: ModuleNotFoundError: No module named 'jsonschema.compat'
  Body: drf_yasg==1.20.0
  swagger_spec_validator==2.7.3
  
  ```python
  Internal Server Error: /
  Traceback (most recent call last):
    File "/usr/local/lib/python3.9/site-packages/django/core/handlers/exception.py", line 47, in inner
      response = get_response(request)
    File "/usr/local/lib/python3.9/site-packages/django/core/handlers/base.py", line 204, in _get_response
      response = response.render()
    File "/usr/local/lib/python3.9/site-packages/django/template/response.py", line 105, in render
      self.content = self.rendered_content
    File "/usr/local/lib/python3.9/site-packages/rest_framework/response.py", line 70, in rendered_content
      ret = renderer.render(self.data, accepted_media_type, context)
    File "/usr/local/lib/python3.9/site-packages/drf_yasg/renderers.py", line 35, in render
      return codec.encode(data)
    File "/usr/local/lib/python3.9/site-packages/drf_yasg/codecs.py", line 73, in encode
      VALIDATORS[validator](copy.deepcopy(spec))
    File "/usr/local/lib/python3.9/site-packages/drf_yasg/codecs.py", line 29, in _validate_swagger_spec_validator
      from swagger_spec_validator.common import SwaggerValidationError as SSVErr
    File "/usr/local/lib/python3.9/site-packages/swagger_spec_validator/__init__.py", line 8, in <module>
      from swagger_spec_validator.util import validate_spec_url
    File "/usr/local/lib/python3.9/site-packages/swagger_spec_validator/util.py", line 9, in <module>
      from swagger_spec_validator import validator12
    File "/usr/local/lib/python3.9/site-packages/swagger_spec_validator/validator12.py", line 29, in <module>
      from swagger_spec_validator.ref_validators import default_handlers
    File "/usr/local/lib/python3.9/site-packages/swagger_spec_validator/ref_validators.py", line 14, in <module>
      from jsonschema.compat import iteritems
  ModuleNotFoundError: No module named 'jsonschema.compat'
  ```
  