add extra build envs

.travis.yml

@@ -5,20 +5,25 @@ cache:
     - vendor
     - $HOME/.composer/cache
 php:
-  - 5.5
   - 5.6
   - 7.0
   - 7.2
 
 matrix:
   include:
     - php: 5.5
+      dist: trusty
       env: COMPOSER_FLAGS='--prefer-lowest --prefer-stable'
+    - php: 7.0
+      dist: trusty
+      env: COMPOSER_FLAGS='--prefer-lowest --prefer-stable'
+    - php: 5.5
+      dist: trusty
 
 before_script:
   - echo "xdebug.max_nesting_level=1000" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
   - if [[ $TRAVIS_PHP_VERSION = '5.6' ]]; then PHPUNIT_FLAGS="--coverage-clover=coverage.clover"; else PHPUNIT_FLAGS=""; fi
-  - if [[ $TRAVIS_PHP_VERSION != '5.6' ]]; then phpenv config-rm xdebug.ini; fi  
+  - if [[ $TRAVIS_PHP_VERSION != '5.6' ]]; then phpenv config-rm xdebug.ini; fi
   - composer self-update
   - composer update $COMPOSER_FLAGS
 
@@ -27,4 +32,4 @@ script: vendor/phpunit/phpunit/phpunit $PHPUNIT_FLAGS
 after_script:
   - wget https://scrutinizer-ci.com/ocular.phar
   - if [[ $TRAVIS_PHP_VERSION = '5.6' ]]; then php ocular.phar code-coverage:upload --format=php-clover coverage.clover; fi
-  
+