Update "R Programming for Data Science" free link (#2923)

free-programming-books.md

@@ -2177,7 +2177,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [R Packages](http://r-pkgs.had.co.nz) - Hadley Wickham
 * [R Practicals](http://www.columbia.edu/~cjd11/charles_dimaggio/DIRE/resources/R/practicalsBookNoAns.pdf) (PDF)
 * [R Programming](https://en.wikibooks.org/wiki/R_Programming)
-* [R Programming for Data Science](https://leanpub.com/rprogramming) - Roger D. Peng  *(Leanpub account or valid email requested)*
+* [R Programming for Data Science](https://bookdown.org/rdpeng/rprogdatascience) - Roger D. Peng
 * [R Succinctly, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/rsuccinctly) (PDF, Kindle) (email address *requested*, not required)
 * [The caret Package](http://topepo.github.io/caret/index.html) - Max Kuhn
 * [The R Inferno](http://www.burns-stat.com/pages/Tutor/R_inferno.pdf) - Patrick Burns (PDF)