define parameter_names.matrix to fix R-devel issue

in R 4.0 matrices will also inherit from array so we need a matrix method here to avoid the array method getting called instead of the default method

Author: jgabry

DESCRIPTION

@@ -1,8 +1,8 @@
 Package: bayesplot
 Type: Package
 Title: Plotting for Bayesian Models
-Version: 1.7.0.9000
-Date: 2019-05-22
+Version: 1.7.1
+Date: 2019-11-25
 Authors@R: c(person("Jonah", "Gabry", role = c("aut", "cre"), email = "jsg2201@columbia.edu"),
              person("Tristan", "Mahr", role = "aut"),
              person("Paul-Christian", "Bürkner", role = "ctb"),

NEWS.md

@@ -1,11 +1,19 @@
 <!-- See http://style.tidyverse.org/news.html for advice on writing news -->
 
-# bayesplot 1.7.0.9000
+
+<!-- 
+# bayesplot 1.7.1.9000
 
 (GitHub issue/PR numbers in parentheses)
 
-<!-- Items for next release go here-->
+Items for next release go here
+-->
+
+# bayesplot 1.7.1
 
+CRAN requested release to fix error at
+https://cran.r-project.org/web/checks/check_results_bayesplot.html due to
+matrices also inheriting from "array" in R 4.0
 
 # bayesplot 1.7.0
 

R/helpers-mcmc.R

@@ -310,9 +310,9 @@ parameter_names.array <- function(x) {
 parameter_names.default <- function(x) {
   colnames(x) %||% abort("No parameter names found.")
 }
-# parameter_names.matrix <- function(x) {
-#   colnames(x) %||% abort("No parameter names found.")
-# }
+parameter_names.matrix <- function(x) {
+  colnames(x) %||% abort("No parameter names found.")
+}
 
 # Check if an object is a 3-D array
 is_3d_array <- function(x) {