Prefer using override instead of virtual in qdbusxml2cpp

In C++ 11 override keyword was introduced to allow overridden functions
to be marked appropriately. Its presence allows compilers to verify that
an overridden function correctly overrides a base class implementation.
This can be useful as compilers can generate a compile time error when:
- The base class implementation function signature changes.
- The user has not created the override with the correct signature.

This commit improves the D-Bus interface code generation.

Change-Id: I0353575c3f70277d04e41b8fa0096c1b2b28058a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/tools/qdbusxml2cpp/qdbusxml2cpp.cpp

@@ -950,7 +950,7 @@ void QDBusXmlToCpp::writeAdaptor(const QString &filename,
            << "        \"\")\n"
               "public:\n"
               "    " << className << "(" << parent << " *parent);\n"
-              "    virtual ~" << className << "();\n\n";
+              "    ~" << className << "() override;\n\n";
 
         if (!parentClassName.isEmpty())
             hs << "    inline " << parent << " *parent() const\n"