text: Title: OAuth2 password credential doesn't work in SwaggerUI
  Body: In SwaggerUI which created by flask-restplus, just simple request is working well.
  
  But, if I trying to use oauth2 with password credential then the credential popup doesn't show up.
  
  To make sure this problem, I tried to use SwaggerUI from SwaggerUI project page with Swagger json; /swagger.json.
  
  And it worked. But the other SwaggerUI that created by flask-restplus still doesn't work.
  
  I think, something wrong in swagger template at flask-restplus on pip-py3.
  
  Please check it.
  