Switch to local phpunit

This ensures consistency across platforms and testing by using the same version of PHPUnit, rather than whatever is globally installed by the system.

.travis.yml

@@ -19,7 +19,7 @@ before_script:
   - travis_retry composer update ${COMPOSER_FLAGS} --no-interaction --prefer-source
 
 script:
-  - phpunit --coverage-text --coverage-clover=coverage.clover
+  - vendor/bin/phpunit --coverage-text --coverage-clover=coverage.clover
 
 after_script:
   - if [[ $TRAVIS_PHP_VERSION != 'hhvm' && $TRAVIS_PHP_VERSION != '7.0' ]]; then php vendor/bin/ocular code-coverage:upload --format=php-clover coverage.clover; fi

composer.json

@@ -33,7 +33,7 @@
         }
     },
     "scripts": {
-        "test": "phpunit"
+        "test": "vendor/bin/phpunit"
     },
     "extra": {
         "branch-alias": {