Merge pull request #27 from M6Web/fix/travis-builds

Remove php5.5 build on travis since it's not supported anymore by PHP itself

.travis.yml

@@ -1,14 +1,13 @@
 language: php
 
 php:
-  - 5.5
   - 5.6
   - 7.0
   - 7.1
 
 before_script:
   - wget http://getcomposer.org/composer.phar
-  - php composer.phar install --dev
+  - php composer.phar install
 
 script:
   - vendor/bin/atoum