update preview link

Author: kevinushey

27-RcppParallel/README.md

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 This repository houses the materials used for the `RcppParallel` webinar delivered on August 31st, 2016.
 
-[Click here](https://rawgit.com/kevinushey/RcppParallel-webinar-2016/master/slides.html) to quickly preview the slides online.
+[Click here](https://rawgit.com/rstudio/webinars/master/27-RcppParallel/slides.html) to quickly preview the slides online.
 
 Visit the [RcppParallel webpage](https://rcppcore.github.io/RcppParallel/) to learn more!