fix demo link in formatters doc (#311)

Co-authored-by: Nathan Bierema <nbierema@gmail.com>

Author: johnrees

docs/formatters.md

@@ -1,6 +1,6 @@
 # Formatters
 
-Some formatters are included that let you convert a JSON delta into other formats, you can see some of these used in the [Live Demo](http://benjamine.github.com/jsondiffpatch/demo/index.html)
+Some formatters are included that let you convert a JSON delta into other formats, you can see some of these used in the [Live Demo](https://benjamine.github.io/jsondiffpatch/demo/index.html)
 
 ## Html