refine the message of queuing a task (#3437)

### What problem does this PR solve?



### Type of change

- [x] Refactoring

api/db/services/document_service.py

     def begin2parse(cls, docid):
         cls.update_by_id(
             docid, {"progress": random.random() * 1 / 100.,
-                    "progress_msg": "Task dispatched...",
+                    "progress_msg": "Task is queued...",
                     "process_begin_at": get_format_time()
                     })
 

rag/nlp/rag_tokenizer.py

             F += freq
             L += 0 if len(tk) < 2 else 1
             tks.append(tk)
-        F /= len(tks)
+        #F /= len(tks)
         L /= len(tks)
         logging.debug("[SC] {} {} {} {} {}".format(tks, len(tks), L, F, B / len(tks) + L + F))
         return tks, B / len(tks) + L + F