fix related to previous commit of MCMC.py

scenariosAleatoires/MCMC_config.yml

 patches: ../output/PAT_patches/PAT_patches.shp
 target: ../resources/targetPAT.csv
 output_dir: ../output/MCMC
-write_shp: True
+write_data: True
 initial_nb_particles: 1000
 max_iterations: 10
 multiprocessing: False