Drop tests for php 5.6

Author: Christoph Rumpel

.travis.yml

@@ -1,7 +1,6 @@
 language: php
 
 php:
-  - 5.6
   - 7.0
   - 7.1
 
@@ -15,7 +14,7 @@ before_script:
   - travis_retry composer update ${COMPOSER_FLAGS} --no-interaction --prefer-source
 
 script:
-  - vendor/bin/phpunit --coverage-text --coverage-clover=coverage.clover
+  - phpunit --coverage-text --coverage-clover=coverage.clover
 
 after_script:
   - wget https://scrutinizer-ci.com/ocular.phar