fix the build

models/PoissonSolver.cpp

@@ -5,7 +5,7 @@
 #include "analysis/distance.h"
 #include "common/ReadMicroCT.h"
 
-ScaLBL_Poisson::ScaLBL_Poisson(int RANK, int NP, MPI_Comm COMM):
+ScaLBL_Poisson::ScaLBL_Poisson(int RANK, int NP, const Utilities::MPI& COMM):
 rank(RANK), nprocs(NP),timestep(0),timestepMax(0),tau(0),k2_inv(0),tolerance(0),h(0),
 epsilon0(0),epsilon0_LB(0),epsilonR(0),epsilon_LB(0),Vin(0),Vout(0),Nx(0),Ny(0),Nz(0),N(0),Np(0),analysis_interval(0),
 chargeDen_dummy(0),WriteLog(0),