[travis] Allow build to finish as soon as possible

This will allow the entire build to fail if one case failed
without waiting for the remaining cases to finish their tests

.travis.yml

@@ -13,6 +13,7 @@ script:
   - phpcs . --standard=phpcs.xml --warning-severity=0 --extensions=php -p
 
 matrix:
+  fast_finish: true
   allow_failures:
     - php: hhvm
     - php: nightly