App: modernize C++: return braced init list

src/App/GeoFeaturePyImp.cpp

@@ -34,7 +34,7 @@ using namespace App;
 // returns a string which represents the object e.g. when printed in python
 std::string GeoFeaturePy::representation() const
 {
-    return std::string("<GeoFeature object>");
+    return {"<GeoFeature object>"};
 }
 
 PyObject* GeoFeaturePy::getPaths(PyObject * /*args*/)