Merge pull request #55 from php-api-clients/composer-1.8

Require composer 1.8 to solve build failure on prefer-lowest due to incompatible continue call on PHP 7.3+

Author: WyriHaximus

composer.json

@@ -12,6 +12,7 @@
     "php": "^7.2",
     "api-clients/cs-fixer-config": "^1.1.1",
     "clue/block-react": "^1.3",
+    "composer/composer": "^1.8",
     "friendsofphp/php-cs-fixer": "^2.13",
     "infection/infection": "^0.11.4",
     "jakub-onderka/php-console-highlighter": "^0.4",