Updated debian distro from jessie to stretch

.circleci/config.yml

@@ -11,10 +11,10 @@ jobs:
       - run:
          name: base build
          command: |
-           docker pull debian:jessie
+           docker pull debian:stretch
            make base
            mkdir -p ~/docker
-           docker save -o ~/docker/base.tar debian:jessie dockcross/base:latest
+           docker save -o ~/docker/base.tar debian:stretch dockcross/base:latest
       - run:
          name: base test
          command: |