Installing forums bundle with --deployment flag

This will prevent Gemfile.lock from being modified.

playbooks/roles/forum/tasks/deploy.yml

@@ -62,7 +62,7 @@
 # since the process owner needs write access
 # to the rbenv
 - name: install comments service bundle
-  shell: bundle install chdir={{ forum_code_dir }}
+  shell: bundle install --deployment chdir={{ forum_code_dir }}
   sudo_user: "{{ common_web_user }}"
   environment: "{{ forum_environment }}"
   notify: restart the forum service