Fix tests

.travis.yml

@@ -11,12 +11,10 @@ cache:
     - vendor
 
 install:
-  - phpenv config-rm xdebug.ini
-  - composer self-update
+  - phpenv config-rm xdebug.ini || true
   - composer config --global discard-changes true
-  - if [[ ${TRAVIS_PHP_VERSION:0:3} == "5.5" ]]; then composer require --dev --no-update phpunit/phpunit ^4; fi
-  - composer require satooshi/php-coveralls dev-master --dev --no-update
-  - composer update --ignore-platform-reqs
+  - composer install
+  - composer require satooshi/php-coveralls dev-master --dev
   - composer show --installed
 
 script:

composer.json

@@ -22,7 +22,7 @@
         "symfony/yaml": "^3.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^5",
+        "phpunit/phpunit": "^4|^5",
         "friendsofphp/php-cs-fixer": "^1.9",
         "macfja/phar-builder": "^0.2.5"
     },