Drop PHP5.5 support

Author: Corey McCormick

.travis.yml

@@ -1,13 +1,12 @@
 language: php
 sudo: false
 php:
-  - 5.5
   - 5.6
   - 7.0
   - hhvm
 
 before_script:
   - composer install --dev
   - composer update -o
-  
+
 script: phpunit --bootstrap tests/bootstrap.php --configuration phpunit.xml tests