merged branch 2.1.x into master

Author: craue

.travis.yml

@@ -49,6 +49,8 @@ before_script:
   - mkdir -p build/logs
 
 script:
+  # validate composer.json
+  - composer validate --strict --no-check-lock
   # enable Xdebug for code coverage analysis
   - if [ "${TRAVIS_PHP_VERSION}" != 'hhvm' ]; then mv xdebug.ini ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini; fi;
   # run PHPUnit