nextcloud-client: fix icon name in desktop file

The desktop file bundled with nextcloud calls the icon `nextcloud`, but the
icons are named `Nextcloud` and so desktop environments won't find it.

pkgs/applications/networking/nextcloud-client/default.nix

@@ -36,7 +36,10 @@ stdenv.mkDerivation rec {
     "-DINOTIFY_INCLUDE_DIR=${inotify-tools}/include"
   ];
 
-  postInstall = stdenv.lib.optionalString (withGnomeKeyring) ''
+  postInstall = ''
+    sed -i 's/\(Icon.*\)=nextcloud/\1=Nextcloud/g' \
+      $out/share/applications/nextcloud.desktop
+  '' + stdenv.lib.optionalString (withGnomeKeyring) ''
     wrapProgram "$out/bin/nextcloud" \
       --prefix LD_LIBRARY_PATH : ${stdenv.lib.makeLibraryPath [ libgnome_keyring ]}
   '';