Fixed wrong test values

src/electrophysiology/problem/ElphyHexaCube2dProblem.cpp

 #include "ElphyHexaCube2dProblem.hpp"
 
-constexpr std::array<double, 2> potentialValues{12.567334, -84.573689};
+constexpr std::array<double, 2> potentialValues{12.595238, -84.573690};
 
 std::string ElphyHexaCube2dProblem::Evaluate(const Vector &solution) const {
   std::string evaluation{};

src/electrophysiology/problem/ElphyTetraCubeProblem.cpp

 #include "ElphyTetraCubeProblem.hpp"
 
 
-constexpr std::array<double, 2> potentialValues{22.29586486, -84.57236069};
+constexpr std::array<double, 2> potentialValues{23.2810756, -84.572363};
 
 
 std::string ElphyTetraCubeProblem::Evaluate(const Vector &solution) const {