[STYLE] avoid compiler warning: data was defined as a class but its...

[STYLE] avoid compiler warning: data was defined as a class but its implementation says that it is a struct.

src/core/common/WSharedLib.h

@@ -164,7 +164,7 @@ private:
     void* findVariable( const std::string& name ) const;
 
     //! internal data
-    class data;
+    struct data;
 
     //! internal data
     data* m_data;