ksysguard: Add required qtwebkit dependency.

Without this the only the daemon would be built without a GUI.

(cherry picked from commit 7940692)

pkgs/desktops/kde-5/plasma/ksysguard.nix

@@ -1,13 +1,13 @@
 { plasmaPackage, ecm, kdoctools, kconfig
 , kcoreaddons, kdelibs4support, ki18n, kitemviews, knewstuff
-, kiconthemes, libksysguard
+, kiconthemes, libksysguard, qtwebkit
 }:
 
 plasmaPackage {
   name = "ksysguard";
   nativeBuildInputs = [ ecm kdoctools ];
   propagatedBuildInputs = [
     kconfig kcoreaddons kitemviews knewstuff kiconthemes libksysguard
-    kdelibs4support ki18n
+    kdelibs4support ki18n qtwebkit
   ];
 }