Merge branch 'nightlies-docker-image' into 'master'

Use the new docker image in nightlies as well

Closes #61

See merge request !184

bob/devtools/data/gitlab-ci/nightlies.yaml

@@ -40,21 +40,24 @@ stages:
     - bdt ci nightlies -vv order.txt
     - bdt ci clean -vv
 
-build_linux_36:
+.build_linux_template:
   extends: .build_template
-  variables:
-    PYTHON_VERSION: "3.6"
   tags:
     - docker
+  image: docker.idiap.ch/bob/docker-images/c3i-linux-64
+
+
+build_linux_36:
+  extends: .build_linux_template
+  variables:
+    PYTHON_VERSION: "3.6"
   cache:
     key: 'build-py36'
 
 build_linux_37:
-  extends: .build_template
+  extends: .build_linux_template
   variables:
     PYTHON_VERSION: "3.7"
-  tags:
-    - docker
   cache:
     key: 'build-py37'