chore: drop php8

php_codesniffer does not support phpunit 9.3 yet

Author: kenjis

.travis.yml

@@ -33,7 +33,7 @@ matrix:
         - php: '7.2'
         - php: '7.3'
         - php: '7.4'
-        - php: '8.0'
+        # - php: '8.0'
         # aliased to a recent hhvm version
         # - php: 'hhvm'
         # php nightly