smaller tresca threshold

dune/tectonic/data-structures/friction/frictionpotential.hh

@@ -151,7 +151,7 @@ class Tresca : public FrictionPotential {
   }
 
   double regularity(double V) const override {
-    if (std::abs(V) < 1e-14) // TODO
+    if (std::abs(V) < 1e-7) // TODO
         return std::numeric_limits<double>::infinity();
 
     return std::abs(second_deriv(V));