gnu: r-rstudioapi: Update to 0.13.

* gnu/packages/statistics.scm (r-rstudioapi): Update to 0.13.
[native-inputs]: Add r-knitr.

gnu/packages/statistics.scm

@@ -2433,14 +2433,16 @@ pure C implementation of the Git core methods.")
 (define-public r-rstudioapi
   (package
     (name "r-rstudioapi")
-    (version "0.11")
+    (version "0.13")
     (source (origin
               (method url-fetch)
               (uri (cran-uri "rstudioapi" version))
               (sha256
                (base32
-                "0srh0m4mw4k6s7spwb84l4cx4xnn04cp5cjxi0fwza7bwavpzq0k"))))
+                "12vdfzzjc6mv4h105l8cp108j3hjk0mqmg23m6mqr3jarfymphxa"))))
     (build-system r-build-system)
+    (native-inputs
+     `(("r-knitr" ,r-knitr)))
     (home-page "https://cran.r-project.org/web/packages/rstudioapi")
     (synopsis "Safely access the RStudio API")
     (description