prefer-dist when installing composer deps

Author: AydinHassan

.travis.yml

@@ -17,7 +17,7 @@ before_install:
   - if [ "$SYMFONY_VERSION" != "" ]; then composer require --dev --no-update symfony/symfony=$SYMFONY_VERSION; fi
 
 install:
-  - composer update $COMPOSER_FLAGS --prefer-source --optimize-autoloader
+  - composer update $COMPOSER_FLAGS --prefer-dist --optimize-autoloader
 
 before_script:
   - mkdir -p build/logs