add ci config for php 8.0/8.1 and symfony 6

Author: Kleinkind

.travis.yml

@@ -54,6 +54,30 @@ matrix:
         - SYMFONY_VERSION=5.0.*
         - MONOLOG_VERSION=^2.0
 
+    - language: php
+      php: 8.0
+      env:
+        - SYMFONY_VERSION=5.0.*
+        - MONOLOG_VERSION=^2.0
+
+    - language: php
+      php: 8.0
+      env:
+        - SYMFONY_VERSION=6.0.*
+        - MONOLOG_VERSION=^2.0
+
+    - language: php
+      php: 8.1
+      env:
+        - SYMFONY_VERSION=5.0.*
+        - MONOLOG_VERSION=^2.0
+
+    - language: php
+      php: 8.1
+      env:
+        - SYMFONY_VERSION=6.0.*
+        - MONOLOG_VERSION=^2.0
+
 before_script:
   - phpenv config-add travis.php.ini
   - composer self-update