TravisCI does not have Xdebug 2.5

Author: sebastianbergmann

composer.json

@@ -33,7 +33,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^5.7",
-        "ext-xdebug": "^2.5"
+        "ext-xdebug": "^2.1.4"
     },
     "suggest": {
         "ext-xdebug": "^2.5.1"