changing MPI example compilation to use bash

Jenkinsfile_mpi_examples_test

@@ -13,7 +13,7 @@ parallel (
 
          stage ('run example ubuntu')
          {
-          sh "export PATH=\"/usr/local/binutils/bin/:$PATH\" && source $HOME/openfpm_vars_master && cd example && make run"
+          bash "export PATH=\"/usr/local/binutils/bin/:$PATH\" && source $HOME/openfpm_vars_master && cd example && make run"
          }
        }},