Drop Travis configuration

.travis.yml

@@ -1,20 +0,0 @@
-language: php
-php:
-  - 5.6
-  - 7.4
-  - nightly
-
-before_script:
-  - composer self-update
-  - composer install --optimize-autoloader --prefer-dist --no-interaction --no-progress --no-suggest
-
-script:
-  - vendor/bin/robo --no-interaction code:cs --strict
-
-matrix:
-  allow_failures:
-    - php: nightly
-
-cache:
-  directories:
-    - $HOME/.composer/cache