use phive-installed phpunit for test stage

Author: ashnazg

.travis.yml

@@ -12,9 +12,10 @@ matrix:
 install:
   - travis_retry composer install --no-interaction --prefer-dist --optimize-autoloader
   - travis_retry wget https://phar.io/releases/phive.phar
+  - travis_retry php phive.phar --no-progress install --trust-gpg-keys 4AA394086372C20A phpunit
 
 script:
-  - phpunit --no-coverage
+  - ./tools/phpunit --no-coverage
 
 jobs:
   include: