Add php 8 to travis and explode in matrix for tests

.travis.yml

@@ -1,33 +1,42 @@
 language: php
 sudo: false
 
-php:
-  - '7.3'
-  - '7.4'
+cache:
+  directories:
+    - $HOME/.composer/cache/files
 
-env:
-  - SYMFONY_VERSION="3.4.*"
-  - SYMFONY_VERSION="4.4.*"
-  - SYMFONY_VERSION="5.0.*"
-  - SYMFONY_VERSION="5.1.*"
-  - SYMFONY_VERSION="5.2.*"
+matrix:
+  fast_finish: true
+  include:
+    - php: 7.3
+      env: SYMFONY_VERSION="3.4.*"
+    - php: 7.3
+      env: SYMFONY_VERSION="4.4.*"
+    - php: 7.3
+      env: SYMFONY_VERSION="5.1.*"
+    - php: 7.3
+      env: SYMFONY_VERSION="5.2.*"
+    - php: 7.4
+      env: SYMFONY_VERSION="3.4.*"
+    - php: 7.4
+      env: SYMFONY_VERSION="4.4.*"
+    - php: 7.4
+      env: SYMFONY_VERSION="5.1.*"
+    - php: 7.4
+      env: SYMFONY_VERSION="5.2.*"
+    - php: 8.0
+      env: SYMFONY_VERSION="5.2.*" COMPOSER_FLAGS="--ignore-platform-reqs"
 
-before_script:
-  - composer self-update
-  - sed -i -e "s/\^3\.4[|]\^4\.3[|]\^5\.0/$SYMFONY_VERSION/g" composer.json
-  - composer install --dev --prefer-dist --no-interaction -o
+install:
+  - composer require --prefer-dist --no-interaction ${COMPOSER_FLAGS} symfony/symfony:${SYMFONY_VERSION}
 
 script:
   - ./vendor/bin/phpcs -p --standard=./ruleset.xml
-  - ./vendor/bin/phpunit -c phpunit.xml.dist --coverage-clover=coverage.xml
+  - XDEBUG_MODE=coverage ./vendor/bin/phpunit -c phpunit.xml.dist --coverage-clover=coverage.xml
 
 after_success:
   - bash <(curl -s https://codecov.io/bash)
 
-cache:
-  directories:
-    - $COMPOSER_CACHE_DIR
-
 notifications:
   email:
     - [email protected]