Add PHP 8 / nightly in Travis matrix

.travis.yml

@@ -19,6 +19,7 @@ before_install:
 
 install:
     - travis_retry composer install
+    - if [[ $TRAVIS_PHP_VERSION = nightly ]]; then phpenv global 7.1; ./vendor/bin/simple-phpunit install; phpenv global nightly; fi
 
 script: ./vendor/bin/simple-phpunit
 
@@ -29,6 +30,8 @@ jobs:
         - php: 7.2
         - php: 7.3
         - php: 7.4
+        - php: nightly
+          env: SYMFONY_PHPUNIT_VERSION=7.2
         - stage: integration tests
           php: 7.3
           script: ./drupal_test.sh