removed flask-restplus and replaced with flask-restx

backend/api/room_api.py

@@ -6,7 +6,7 @@ For example: listing of available auth providers or registration of users.
 Login through API does not start a new session, but instead returns JWT.
 """
 from flask_jwt_extended import jwt_required
-from flask_restplus import fields, Resource
+from flask_restx import fields, Resource
 from sqlalchemy import exc
 
 from backend import db, app