Add gitlab CI configuration.

.gitlab-ci.yml

@@ -5,8 +5,12 @@ stages:
   - deploy
 
 before_script:
-  - apt-get install make
-  - apt-get install g++
+  - apt-get update -yqq \
+    && apt-get install -yqq --no-install-recommends
+    make
+    g++
+    && apt-get autoremove -yqq --purge
+    && apt-get clean
 
 unittests:
   stage: test