fix travis

Author: Jens Schulze

.travis.yml

@@ -1,6 +1,5 @@
 language: php
 php:
-- "5.5"
 - "5.6"
 - "7.0"
 - "7.1"
@@ -17,8 +16,8 @@ cache:
 
 before_script:
 - PHP=$TRAVIS_PHP_VERSION
-- if [ $PHP == '5.5' ] ; then composer update -o --ignore-platform-reqs --prefer-lowest --prefer-dist; fi
-- if [ $PHP != '5.5' ] ; then composer install -o --prefer-dist; fi
+- if [ $PHP == '5.6' ] ; then composer update -o --ignore-platform-reqs --prefer-lowest --prefer-dist; fi
+- if [ $PHP != '5.6' ] ; then composer install -o --prefer-dist; fi
 
 script:
 - vendor/bin/phpunit