[DEV] change NULL ==> nullptr

sources/appl/Gui/ViewerManager.h

@@ -52,7 +52,7 @@ namespace appl {
 			 * @brief keep the resource pointer.
 			 * @note Never free this pointer by your own...
 			 * @param[in] _filename Name of the configuration file.
-			 * @return pointer on the resource or NULL if an error occured.
+			 * @return pointer on the resource or nullptr if an error occured.
 			 */
 			static ewol::object::Shared<appl::ViewerManager> keep();
 	};