Change debian version for environments
Change debian version for environments

- Debian version changed to jessie to get packages for environments

pythia-project/pythia-core,pythia-project/pythia-core,pythia-project/pythia-core,pythia-project/pythia,pythia-project/pythia,pythia-project/pythia-core,pythia-project/pythia,pythia-project/pythia,pythia-project/pythia,pythia-project/pythia,pythia-project/pythia-core,pythia-project/pythia-core