add php 8 in travis config + bump 7.3 to 7.4

.travis.yml

@@ -0,0 +1,59 @@
+language: php
+
+cache:
+  directories:
+    - $HOME/.composer/cache/files
+
+branches:
+  except:
+    - /^analysis-.*$/
+
+env:
+  global:
+    - TEST_COMMAND="composer test"
+
+matrix:
+  fast_finish: true
+  include:
+    # Minimum supported Symfony version and latest PHP version
+    - php: 7.4
+      env: COMPOSER_FLAGS="--prefer-stable --prefer-lowest" SYMFONY_DEPRECATIONS_HELPER="weak"
+
+      # Test the latest stable release
+    - php: 7.1
+    - php: 7.2
+    - php: 7.3
+    - php: 8.0
+    - php: 8.1
+
+      # Test LTS versions
+    - php: 7.4
+      env: DEPENDENCIES="dunglas/symfony-lock:^3"
+    - php: 7.4
+      env: DEPENDENCIES="dunglas/symfony-lock:^4"
+
+      # Latest commit to master
+    - php: 7.4
+      env: STABILITY="dev"
+
+  allow_failures:
+    # dev stability is allowed to fail.
+    - env: STABILITY="dev"
+
+before_install:
+  - if [[ $COVERAGE != true ]]; then phpenv config-rm xdebug.ini || true; fi
+  - if ! [ -z "$STABILITY" ]; then composer config minimum-stability ${STABILITY}; fi;
+  - if ! [ -v "$DEPENDENCIES" ]; then composer require --no-update ${DEPENDENCIES}; fi;
+
+install:
+  # To be removed when this issue will be resolved: https://github.com/composer/composer/issues/5355
+  - if [[ "$COMPOSER_FLAGS" == *"--prefer-lowest"* ]]; then composer update --prefer-dist --no-interaction --prefer-stable --quiet; fi
+  - COMPOSER_MEMORY_LIMIT=-1 composer update ${COMPOSER_FLAGS} --prefer-dist --no-interaction
+
+script:
+  - composer validate --strict --no-check-lock
+  - $TEST_COMMAND
+
+after_success:
+  - if [[ $COVERAGE = true ]]; then wget https://scrutinizer-ci.com/ocular.phar; fi
+  - if [[ $COVERAGE = true ]]; then php ocular.phar code-coverage:upload --format=php-clover build/coverage.xml; fi