Improve error message and fix typo, closes #3657

src/Composer/Factory.php

@@ -167,7 +167,7 @@ class Factory
 
         foreach ($config->getRepositories() as $index => $repo) {
             if (is_string($repo)) {
-                throw new \UnexpectedValueException('Repositories should be an array of repository defintions, only a single repository was given');
+                throw new \UnexpectedValueException('"repositories" should be an array of repository definitions, only a single repository was given');
             }
             if (!is_array($repo)) {
                 throw new \UnexpectedValueException('Repository "'.$index.'" ('.json_encode($repo).') should be an array, '.gettype($repo).' given');