gnu: r: Use gfortran-4.9.

* gnu/packages/statistics.scm (r)[inputs]: Replace gfortran-4.8 with
  gfortran-4.9.

gnu/packages/statistics.scm

@@ -90,7 +90,7 @@ (define-public r
     (inputs
      `(("atlas" ,atlas) ; --with-blas
        ("cairo" ,cairo)
-       ("gfortran" ,gfortran-4.8)
+       ("gfortran" ,gfortran-4.9)
        ("icu4c" ,icu4c)
        ("icedtea6" ,icedtea6 "jdk")
        ("lapack" ,lapack)