gnu: r-rserve: Fix upstream hash mismatch.

The tarball was modified upstream.  It appears that the ‘1.8-6’ version
that was packaged was actually a development snapshot.  In Rserve/NEWS:

    -1.8-6      (under development)
    +1.8-6      2020-06-11

The only difference appears to be in the build system:

    proxy: linking no longer hard-codes `-lssl` (it effectively
    failed compilation when SSL was not available).

as the build output does not appear to contain new or changed code.

* gnu/packages/cran.scm (r-rserve)[source]: Update sha256.

Change-Id: Ib32ecbdcbab1a4992f61215f94f1625e316edda2

gnu/packages/cran.scm

@@ -34842,8 +34842,7 @@ (define-public r-rserve
        (uri (string-append "http://www.rforge.net/Rserve/snapshot/Rserve_"
                            version ".tar.gz"))
        (sha256
-        (base32
+        (base32 "0z1xvx8ifvlwfl3rf1wwhpbwp4ivh7sn71xhlqihqpsclpmljg8p"))))
-         "017kkzv9lxlz9qhg3gprrf1wcyflxrif6wjk27x9b4bdzylw6bsx"))))
     (build-system r-build-system)
     (arguments
      `(#:phases