Use utf8 encoding in Jupyter example

mermaid.ink can render some UTF-8 characters

packages/mermaid/src/docs/config/Tutorials.md

@@ -56,7 +56,7 @@ from IPython.display import Image, display
 import matplotlib.pyplot as plt
 
 def mm(graph):
-  graphbytes = graph.encode("ascii")
+    graphbytes = graph.encode("utf8")
     base64_bytes = base64.b64encode(graphbytes)
     base64_string = base64_bytes.decode("ascii")
     display(Image(url="https://mermaid.ink/img/" + base64_string))