Fixing test for GCC5

src/FiniteDifference/eq_unit_test.hpp

src/FiniteDifference/eq_unit_test_3d.hpp

...lver<double>_lid_driven_cavity_3d_p1_grid_0_test_GCC5.vtk

...lver<double>_lid_driven_cavity_3d_p2_grid_0_test_GCC5.vtk

...lver<double>_lid_driven_cavity_3d_p2_grid_1_test_GCC5.vtk

...lver<double>_lid_driven_cavity_3d_p3_grid_0_test_GCC5.vtk

...lver<double>_lid_driven_cavity_3d_p3_grid_1_test_GCC5.vtk

...lver<double>_lid_driven_cavity_3d_p3_grid_2_test_GCC5.vtk

...lver<double>_lid_driven_cavity_3d_p1_grid_0_test_GCC5.vtk

...lver<double>_lid_driven_cavity_3d_p2_grid_0_test_GCC5.vtk

...lver<double>_lid_driven_cavity_3d_p2_grid_1_test_GCC5.vtk

...lver<double>_lid_driven_cavity_3d_p3_grid_2_test_GCC5.vtk

...fpack_solver<double>_lid_driven_cavity_p1_grid_0_test.vtk

...fpack_solver<double>_lid_driven_cavity_p2_grid_0_test.vtk