Workaround Travis Xdebug < 2.3

Maks3w · sebastianbergmann · commit bb5889284415 · 2015-11-06T11:11:30.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -3,6 +3,10 @@ language: php
 php:
     - 5.6
 
+install:
+    - pecl install xdebug
+    - php --version
+
 before_script:
     - COMPOSER_ROOT_VERSION=dev-master composer install --prefer-source
 
