add GitLab CI

.gitlab-ci.yml

+# This file is a template, and might need editing before it works on your project.
+# Select image from https://hub.docker.com/_/php/
+image: php:7.2
+
+# Select what we should cache between builds
+cache:
+  paths:
+  - vendor/
+
+before_script:
+# Install PHP extensions
+- docker-php-ext-install mbstring mcrypt pdo_pgsql curl json intl gd xml zip bz2 opcache
+# Install and run Composer
+- curl -sS https://getcomposer.org/installer | php
+- php composer.phar install
+
+test:
+  before_script:
+    - composer install --no-interaction --prefer-dist
+
+  script:
+    - vendor/bin/tester ./tests/cases
+    - vendor/bin/phpstan analyse --no-progress --level 7 src/