bump version of phpunit

Author: jsteemann

tests/travis/setup_arangodb.sh

@@ -33,8 +33,8 @@ mv phpunit-6.0.phar ./phpunit
 fi
 
 if [[ "$TRAVIS_PHP_VERSION" == "8.0" ]] ; then 
-wget "https://phar.phpunit.de/phpunit-9.0.phar"
-mv phpunit-9.0.phar ./phpunit
+wget "https://phar.phpunit.de/phpunit-9.5.phar"
+mv phpunit-9.5.phar ./phpunit
 fi
 
 if [[ "$TRAVIS_PHP_VERSION" == "hhvm" ]] ; then