update nbviewer url

Author: jefferyUstc

README.md

@@ -5,7 +5,7 @@ Light Weighted dotplot drawer
 
 # Tutorial
 
-Examples of dotplot can be found [tutorial](https://nbviewer.jupyter.org/github/jefferyUstc/python-dotplot/blob/main/tutorial/tutorials.ipynb)
+Examples of dotplot can be found [tutorial](https://nbviewer.jupyter.org/github/jefferyUstc/python-dotplot/blob/main/tutorial/tutorials.ipynb?flush_cache=True)
 
 # Installation
 ```shell script