Use a better way to disable xdebug

.travis.yml

@@ -47,7 +47,7 @@ matrix:
     - php: hhvm
 
 before_script:
-  - rm -f ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini
+  - phpenv config-rm xdebug.ini
   - composer self-update
   - if [ -n "$GH_TOKEN" ]; then composer config github-oauth.github.com ${GH_TOKEN}; fi;
   - composer install --prefer-dist --no-interaction