[examples] Fix CDN live preview demo

Author: oliviertassinari

examples/material-ui-via-cdn/README.md

@@ -23,7 +23,7 @@ The client has to download the entire library, regardless of which components ar
 
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-[The live preview.](https://rawcdn.githack.com/mui/material-ui/master/examples/material-ui-via-cdn/index.html)
+[The live preview.](https://raw.githack.com/mui/material-ui/master/examples/material-ui-via-cdn/index.html)
 
 ## What's next?