Add gitlab CI

.gitlab-ci.yml

+image: docker:stable
+services:
+- docker:dind
+
+stages:
+- test
+
+test:
+  image: ruby:2.5.1
+  tags:
+  - enote-docker
+  stage: test
+  script:
+  - echo "Running tests"
+  - echo ./scripts/run-tests.sh
+  - echo "$(pwd)"
+  - bundle install
+  - bundle exec rake test
+