Enhancement: Validate composer.json on CircleCI

Author: localheinz

.circleci/config.yml

@@ -14,6 +14,9 @@ workflows:
 php-docker-template: &php-docker-template
   steps:
     - checkout
+    - run:
+        name: validate composer.json
+        command: composer validate
     - run:
         name: install current dependencies
         command: composer install --no-progress