Use relpath for merge-dev.php arguments

Author: schmengler

.travis/before_script.sh

@@ -29,7 +29,7 @@ composer config repositories.travis_to_test git https://github.com/$TRAVIS_REPO_
 composer require ${COMPOSER_PACKAGE_NAME}:dev-${TRAVIS_BRANCH}\#{$TRAVIS_COMMIT}
 
 # Install dev dependencies of module
-php ../.travis/merge-dev.php vendor/$COMPOSER_PACKAGE_NAME/composer.json composer.json | tee composer.json
+php ../.travis/merge-dev.php $(realpath vendor/$COMPOSER_PACKAGE_NAME/composer.json) $(realpath composer.json) | tee composer.json
 composer update
 
 # prepare for test suite