update R2 ref

Author: avehtari

R/bayes_R2.R

@@ -18,8 +18,8 @@
 #'
 #'
 #' @references
-#' Andrew Gelman, Ben Goodrich, Jonah Gabry, and Aki Vehtari (2018). R-squared
-#' for Bayesian regression models. *The American Statistician*, to appear.
+#' Andrew Gelman, Ben Goodrich, Jonah Gabry, and Aki Vehtari (2019). R-squared
+#' for Bayesian regression models. *The American Statistician*, 73(3):307-309.
 #' DOI: 10.1080/00031305.2018.1549100.
 #' ([Preprint](http://www.stat.columbia.edu/~gelman/research/published/bayes_R2_v3.pdf),
 #' [Notebook](https://avehtari.github.io/bayes_R2/bayes_R2.html))