[Cleanup] Fix name: Normal stress != traction

src/assemblers.cc

@@ -114,10 +114,10 @@ void MyAssembler<GridView, dimension>::assembleWeightedNormalStress(
   Vector traction;
   // Note: We assume v = 0 here so that there is no viscous
   // contribution to the stress.
-  PointTractionBoundaryAssembler<Grid> weightedNormalStressBoundaryAssembler(
+  PointTractionBoundaryAssembler<Grid> weightedTractionBoundaryAssembler(
       youngModulus, poissonRatio, &displacementFunction, 1);
-  vertexAssembler.assembleBoundaryFunctional(
-      weightedNormalStressBoundaryAssembler, traction, frictionalBoundary);
+  vertexAssembler.assembleBoundaryFunctional(weightedTractionBoundaryAssembler,
+                                             traction, frictionalBoundary);
 
   std::vector<typename Vector::block_type> normals;
   frictionalBoundary.getNormals(normals);