Use Composer 1

This bundle might have several issues with Composer 2, let's see if we
can fix the build for current contributions until Composer 2
compatibility is contributed.

Author: greg0ire

.travis.yml

@@ -20,11 +20,11 @@ env:
     - COMPOSER_MEMORY_LIMIT=-1
 
 before_install:
+  - composer self-update --1
   - mv ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini{,.disabled} || echo "xdebug not available"
   - composer global require --no-progress --no-scripts --no-plugins symfony/flex dev-master
 
 install:
-  - composer self-update
   - pecl install -f mongodb-${DRIVER_VERSION}
   - if [[ -z ${REQUIRE_SYMFONY_MESSENGER} ]]; then composer require --dev symfony/messenger --no-update; fi
   - composer update ${COMPOSER_FLAGS}