Fixing Travis build

Author: moufmouf

.travis.yml

@@ -4,7 +4,8 @@ php:
   - 7.1
 env:
   global:
-  - DEFAULT_COMPOSER_FLAGS="--no-interaction --no-progress --optimize-autoloader"
+  # We need to prefer source to get PHPStan test directory. Otherwise, it is removed from ZIP
+  - DEFAULT_COMPOSER_FLAGS="--no-interaction --no-progress --optimize-autoloader --prefer-source"
   - TASK_TESTS=1
   - TASK_TESTS_COVERAGE=0
   - TASK_CS=1
@@ -18,8 +19,9 @@ cache:
 before_install:
 - travis_retry composer global require $DEFAULT_COMPOSER_FLAGS hirak/prestissimo
 install:
-- travis_retry composer install $DEFAULT_COMPOSER_FLAGS $COMPOSER_FLAGS
+- travis_retry composer update $DEFAULT_COMPOSER_FLAGS $COMPOSER_FLAGS
 - composer info -D | sort
+- mkdir tmp
 script:
 - vendor/bin/phpunit --verbose;
 after_success: