Ignore platform reqs for PHP nightly Travis build

Author: kylekatarnls

.travis.yml

@@ -4,14 +4,18 @@ php:
   - 7.2
   - 7.3
   - 7.4
-  - nightly
+
+matrix:
+  include:
+    - php: nightly
+      env: COMPOSER_FLAGS='--ignore-platform-reqs'
 
 before_script:
   - curl -L https://codeclimate.com/downloads/test-reporter/test-reporter-latest-linux-amd64 > ./cc-test-reporter
   - chmod +x ./cc-test-reporter
   - ./cc-test-reporter before-build
   - travis_retry composer self-update
-  - travis_retry composer install --no-interaction --prefer-source --dev
+  - travis_retry composer install --no-interaction --prefer-source --dev $COMPOSER_FLAGS
 
 script:
   - vendor/bin/phpunit --verbose --coverage-text --coverage-clover=coverage.xml