try using global phpunit

Author: ashnazg

.travis.yml

@@ -11,18 +11,18 @@ matrix:
 
 install:
   - travis_retry composer install --no-interaction --prefer-dist --optimize-autoloader
+  - travis_retry composer global require phpunit/phpunit # cannot use phpunit.phar or require-dev, because this package is a phpunit dep
   - travis_retry wget https://phar.io/releases/phive.phar
-  - travis_retry composer require --dev phpunit/phpunit # cannot trust phpunit.phar, because this package is itself in that phar..."
 
 script:
-  - ./vendor/bin/phpunit --no-coverage
+  - /home/travis/.composer/vendor/bin/phpunit --no-coverage
 
 jobs:
   include:
     - stage: coverage
       php: 7.1
       script:
-        - ./vendor/bin/phpunit
+        - /home/travis/.composer/vendor/bin/phpunit
       after_script:
         - travis_retry php phive.phar --no-progress install --trust-gpg-keys E82B2FB314E9906E php-coveralls/php-coveralls && ./tools/php-coveralls --verbose
         - travis_retry wget https://scrutinizer-ci.com/ocular.phar && php ocular.phar code-coverage:upload --format=php-clover build/logs/clover.xml