Travis: use older version of PHPUnit

.travis.yml

@@ -17,6 +17,8 @@ notifications:
 before_script:
   # PHP_CodeSniffer
   - curl -L -o phpcs.phar https://squizlabs.github.io/PHP_CodeSniffer/phpcs.phar
+  # PHPUnit - manually download old version so that it works on PHP 7
+  - curl -L -o phpunit.phar https://phar.phpunit.de/phpunit-4.8.35.phar
   # Basic config required for PHPUnit
   - cp qa-tests/phpunit-qa-config.php qa-config.php
 
@@ -24,4 +26,4 @@ script:
   # PHP_CodeSniffer
   - php phpcs.phar --report=emacs --extensions=php --standard=qa-tests/phpcs/ruleset.xml .
   # PHPUnit
-  - phpunit --bootstrap qa-tests/autoload.php qa-tests
+  - php phpunit.phar --bootstrap qa-tests/autoload.php qa-tests