Update binder link

Author: martinRenou

README.md

@@ -1,7 +1,7 @@
 
 # ipycanvas
 
-[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/martinRenou/ipycanvas/master?filepath=examples)
+[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/martinRenou/ipycanvas/stable?filepath=examples)
 
 Interactive widgets library exposing the [browser's Canvas API](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API) to Python. There are some API differences though: