MNT Add PHP 8 build

.travis.yml

@@ -13,13 +13,15 @@ env:
 matrix:
   include:
     - php: 7.1
-      env: DB=MYSQL
+      env: DB=MYSQL COMPOSER_ARG=--prefer-lowest
     - php: 7.2
       env: DB=PGSQL
     - php: 7.3
       env: DB=MYSQL
     - php: 7.4
       env: DB=MYSQL
+    - php: nightly
+      env: DB=MYSQL COMPOSER_ARG=--ignore-platform-reqs
 
 before_script:
   - phpenv rehash
@@ -28,7 +30,7 @@ before_script:
   - composer validate
   - composer require --no-update silverstripe-themes/simple:~3.2.0
   - if [[ $DB == PGSQL ]]; then composer require silverstripe/postgresql:2.x-dev --no-update; fi
-  - composer install --prefer-source --no-interaction --no-progress --no-suggest --optimize-autoloader --verbose --profile
+  - composer update --prefer-source --no-interaction --no-progress --no-suggest --optimize-autoloader --verbose --profile $COMPOSER_ARG
 
   # Validate cow schema
   - composer global require silverstripe/cow ^2

composer.json

@@ -5,6 +5,7 @@
     "homepage": "http://silverstripe.org",
     "license": "BSD-3-Clause",
     "require": {
+        "php": "^7.1 || ^8",
         "silverstripe/recipe-plugin": "^1.2",
         "silverstripe/recipe-core": "4.x-dev",
         "silverstripe/admin": "1.x-dev",
@@ -19,7 +20,7 @@
         "silverstripe/versioned": "1.x-dev"
     },
     "require-dev": {
-        "phpunit/phpunit": "^5.7",
+        "sminnee/phpunit": "^5.7",
         "sminnee/phpunit-mock-objects": "^3.4.5"
     },
     "extra": {