AttributeError: 'OpenAPIConverter' object has no attribute 'fields2parameters'

Suddenly, I am facing issue with flask-apispec and the error looks like this

```
docs.register(url.resource)
File "/usr/local/lib/python3.7/site-packages/flask_apispec/extension.py", line 121, in register
resource_class_args, resource_class_kwargs)
File "/usr/local/lib/python3.7/site-packages/flask_apispec/extension.py", line 68, in _defer
bound()
File "/usr/local/lib/python3.7/site-packages/flask_apispec/extension.py", line 143, in _register
resource_class_kwargs=resource_class_kwargs,
File "/usr/local/lib/python3.7/site-packages/flask_apispec/apidoc.py", line 42, in convert
return [self.get_path(rule, target, **kwargs) for rule in rules]
File "/usr/local/lib/python3.7/site-packages/flask_apispec/apidoc.py", line 42, in
return [self.get_path(rule, target, **kwargs) for rule in rules]
File "/usr/local/lib/python3.7/site-packages/flask_apispec/apidoc.py", line 53, in get_path
for method, view in six.iteritems(operations)
File "/usr/local/lib/python3.7/site-packages/flask_apispec/apidoc.py", line 54, in
if method.lower() in (set(valid_methods) - {'head'})
File "/usr/local/lib/python3.7/site-packages/flask_apispec/apidoc.py", line 66, in get_operation
'parameters': self.get_parameters(rule, view, docs, parent),
File "/usr/local/lib/python3.7/site-packages/flask_apispec/apidoc.py", line 92, in get_parameters
converter = openapi.fields2parameters
AttributeError: 'OpenAPIConverter' object has no attribute 'fields2parameters'
```

Libraries used is:

Flask==0.10.1
flask-apispec==0.8.5
Flask-RESTful==0.3.6
marshmallow==2.8.0
webargs==5.5.2

Any solution for this! I have already tried to bump flask-apispec/marshmallow and webargs but no luck

Start with flask_apispec/apidoc.py, especially get_parameters, and trace how the OpenAPIConverter is created through extension.py. Reproduce the AttributeError using the listed Flask, flask-apispec, marshmallow, Flask-RESTful, and webargs versions; done means resource registration completes without this exception and the compatibility case is covered by a test.

Written by the indexing model from the issue text.