Merge pull request #282 from stan-dev/fix-vignette-url

Fix url in vignette

Author: jgabry

vignettes/loo2-example.Rmd

@@ -62,7 +62,7 @@ models.
 ### Roaches data
 
 The example data we'll use comes from Chapter 8.3 of [Gelman and Hill
-(2007)](http://www.stat.columbia.edu/~gelman/arm/). We want to make inferences
+(2007)](https://sites.stat.columbia.edu/gelman/arm/). We want to make inferences
 about the efficacy of a certain pest management system at reducing the number of
 roaches in urban apartments. Here is how Gelman and Hill describe the experiment
 and data (pg. 161):