added this-> for old compilers in a lambda

src/amdis/ProblemStat.inc.hpp

@@ -218,7 +218,7 @@ void ProblemStat<Traits>::createMarker()
     auto newMarker
       = EstimatorMarker<Grid>::createMarker(componentName, tp, estimates_[tp], grid_);
     assert(bool(newMarker));
-    addMarker(std::move(newMarker));
+    this->addMarker(std::move(newMarker));
   });
 }