update Scratch.Rmd with correct URL

Original URL pointed to non-existent site.

Author: StefanBRas

vignettes/articles/Scratch.Rmd

@@ -8,4 +8,4 @@ output:
     toc: yes
 ---
 
-This article can now be found at [`tidymodels.org`](https://www.tidymodels.org/learn/develop/parsnip/).
+This article can now be found at [`tidymodels.org`](https://www.tidymodels.org/learn/develop/models/).