Merge pull request #41 from alister/feature/phpunit-for-pre-php5.6

PHPUnit v5 requires PHP v5.6+. Lock requirements for testing to v4.*

.travis.yml

@@ -41,7 +41,7 @@ matrix:
 before_script:
   - composer selfupdate
   - composer config -g github-oauth.github.com $GITHUB_OAUTH_TOKEN
-  - composer global require phpunit/phpunit --no-update
+  - composer global require phpunit/phpunit:4.* --no-update
   - composer global update --prefer-dist --no-interaction
   - if [ "$SYMFONY_VERSION" != "" ]; then composer require "symfony/symfony:${SYMFONY_VERSION}" --no-update; fi;
   - composer update --prefer-dist --no-interaction $COMPOSER_FLAGS