Update plugin travis.

.travis.yml

@@ -34,7 +34,7 @@ matrix:
 
 before_script:
   - if [[ $PREFER_LOWEST != 1 ]]; then composer install --prefer-source --no-interaction ; fi
-  - if [[ $PREFER_LOWEST == 1 ]]; then composer update --prefer-dist --no-interaction --prefer-lowest --prefer-stable ; fi
+  - if [[ $PREFER_LOWEST == 1 ]]; then composer update --prefer-lowest --prefer-stable --prefer-dist --no-interaction ; fi
 
   - if [[ $CHECKS != 1 ]]; then composer require --dev phpunit/phpunit:"^5.7.14|^6.0"; fi