gnu: r-ggdendro: Update to 0.1.21.

* gnu/packages/statistics.scm (r-ggdendro): Update to 0.1.21.
[propagated-inputs]: Remove r-knitr.
[native-inputs]: Add r-knitr.

gnu/packages/statistics.scm

@@ -1135,18 +1135,19 @@ aesthetic attributes.")
 (define-public r-ggdendro
   (package
     (name "r-ggdendro")
-    (version "0.1-20")
+    (version "0.1.21")
     (source (origin
               (method url-fetch)
               (uri (cran-uri "ggdendro" version))
               (sha256
                (base32
-                "1zzq1hxd0d1qa5hrzwfkdw6fzscpcafbwbpkrb62dm559y8awp0j"))))
+                "0jcjdkhd3wirjgv4v3gb9rw8idyymwhwnxplg3wi8wa3mwr9rhq2"))))
     (build-system r-build-system)
     (propagated-inputs
      `(("r-ggplot2" ,r-ggplot2)
-       ("r-mass" ,r-mass)
-       ("r-knitr" ,r-knitr)))
+       ("r-mass" ,r-mass)))
+    (native-inputs
+     `(("r-knitr" ,r-knitr)))
     (home-page "https://github.com/andrie/ggdendro")
     (synopsis "Create Dendrograms and Tree Diagrams Using ggplot2")
     (description "This is a set of tools for dendrograms and tree plots using