Update CI image to include Docker

.gitlab-ci.yml

@@ -1,5 +1,5 @@
 ---
-image: s3lph/spaceapi-server-ci:20191126-02
+image: s3lph/spaceapi-server-ci:20200620-01
 
 stages:
   - test

package/Dockerfile

@@ -1,6 +1,6 @@
 FROM python:3.8-buster as python
 
 RUN apt update \
-    && apt install -y --no-install-recommends lintian rsync sudo \
+    && apt install -y --no-install-recommends lintian rsync sudo docker.io \
     && pip3 install pycodestyle coverage \
     && rm -rf /var/cache/apt