Always --prefer-stable on Travis

Author: Jean85

.travis.yml

@@ -10,13 +10,12 @@ php:
   - 7.1
   - hhvm
 
-env:
-  - COMPOSER_OPTIONS="--prefer-stable"
-
 matrix:
   include:
+    - php: 5.3
+      env: COMPOSER_OPTIONS="--prefer-lowest"
     - php: 7.0
-      env: COMPOSER_OPTIONS="--prefer-lowest --prefer-stable"
+      env: COMPOSER_OPTIONS="--prefer-lowest"
     - php: 7.1
       env: TEST_COVERAGE=true
   allow_failures:
@@ -31,7 +30,7 @@ before_install:
   - composer self-update
   - if [[ $TEST_COVERAGE ]]; then PHPUNIT_FLAGS="--coverage-clover clover.xml"; fi
 
-install: travis_retry composer update --no-interaction --prefer-dist $COMPOSER_OPTIONS
+install: travis_retry composer update --no-interaction --prefer-dist --prefer-stable $COMPOSER_OPTIONS
 
 script:
   - vendor/bin/phpunit -v $PHPUNIT_FLAGS