Add arg PHP-VERSION in Dockerfile

Dockerfile

-FROM php:cli
+ARG PHP_VERSION
+
+FROM php:${PHP_VERSION}-cli
 
 RUN pecl install xdebug
 

docker-compose.yml

@@ -10,6 +10,8 @@ services:
         volumes:
             - .:/code
         working_dir: /code
+        environment:
+          PHP_VERSION: ${TRAVIS_PHP_VERSION}
         command: bash -c "composer install --prefer-source --no-interaction && php ./vendor/bin/phpunit"
         depends_on:
           - mysql