Update travis config

Author: wtfzdotnet

.travis.yml

@@ -12,6 +12,7 @@ before_script:
   - composer self-update
   - if [ "$SYMFONY_VERSION" != "" ]; then composer require --no-update symfony/config:${SYMFONY_VERSION} symfony/dependency-injection:${SYMFONY_VERSION} symfony/event-dispatcher:${SYMFONY_VERSION} symfony/http-kernel:${SYMFONY_VERSION} symfony/framework-bundle:${SYMFONY_VERSION}; fi;
   - if [ "$SYMFONY_EVENT_DISPATCHER_VERSION" != "" ]; then composer require --no-update symfony/event-dispatcher:${SYMFONY_EVENT_DISPATCHER_VERSION}; fi;
+  - if [ "$SYMFONY_EVENT_DISPATCHER_VERSION" = "" ]; then composer require --no-update symfony/event-dispatcher:{$SYMFONY_VERSION}; fi;
   - composer install --no-interaction --prefer-source --dev
 
 script: phpunit --verbose