Add GitLab CI

• Different set of boxes, there isn't a 7.2 in the current series and doesn't seem like that'll changes
• Correct PHPUnit version for PHP version, as Travis handles

Fixes #2 (closed)

.gitlab-ci.yml

@@ -14,7 +14,7 @@ before_script:
   - apt-get -yqqf install zip unzip subversion mysql-client default-libmysqlclient-dev --fix-missing
 
   # PHP extensions
-  - docker-php-ext-install mbstring mysqli pdo_mysql intl gd zip bz2
+  - docker-php-ext-install mbstring
   - docker-php-ext-enable mbstring mysqli pdo_mysql intl gd zip bz2
 
   # Install Composer