Do not break travis build if disabling Xdebug fails

Resources/travis/prepare_php.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -e
 trap '>&2 echo Error: Command \`$BASH_COMMAND\` on line $LINENO failed with exit code $?' ERR
-echo '==> Disabling xdebug, adjusting memory limit to -1.'
-phpenv config-rm xdebug.ini
+echo '==> Disabling xdebug if needed, adjusting memory limit to -1.'
+phpenv config-rm xdebug.ini || return 0
 echo 'memory_limit = -1' >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
 phpenv rehash;