RegexURLPattern and RegexURLResolver must be changed to URLPattern and URLResolver respectively

[ammarmallik]

Not working for django=2.1.3 & djangorestframework==3.9.0

You need to change this:

• URLPattern and URLResolver on line:3, line:26, line:29 in api_docs.py file.
• pattern.pattern.regex on line:27 in api_docs.py file
• pattern.pattern.regex.pattern on line:43
• parent_pattern.pattern.regex.pattern on line:24, line:39 and line:40 in api_endpoint.py file.

Ref: https://github.com/encode/django-rest-framework/pull/5500