gnu: r-dplyr: Update to 0.8.5.

* gnu/packages/statistics.scm (r-dplyr): Update to 0.8.5.
[native-inputs]: Add r-knitr.

gnu/packages/statistics.scm

@@ -1650,13 +1650,13 @@ (define-public r-tibble
 (define-public r-dplyr
   (package
     (name "r-dplyr")
-    (version "0.8.4")
+    (version "0.8.5")
     (source (origin
               (method url-fetch)
               (uri (cran-uri "dplyr" version))
               (sha256
                (base32
-                "1nd0mmvqjbzbknawa520f64p9zlj9lwdlq0hh7c1mciyy7ah6641"))))
+                "0602b4a9nffxx67q57csqp87nkrv33nn9wlaw1458yys9fzx6l2p"))))
     (build-system r-build-system)
     (propagated-inputs
      `(("r-assertthat" ,r-assertthat)
@@ -1671,6 +1671,8 @@ (define-public r-dplyr
        ("r-rlang" ,r-rlang)
        ("r-tibble" ,r-tibble)
        ("r-tidyselect" ,r-tidyselect)))
+    (native-inputs
+     `(("r-knitr" ,r-knitr)))
     (home-page "https://github.com/hadley/dplyr")
     (synopsis "Tools for working with data frames in R")
     (description