Add back vendor folders for development

vendor/phpunit/php-file-iterator/README.md

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+[![Build Status](https://travis-ci.org/sebastianbergmann/php-file-iterator.svg?branch=master)](https://travis-ci.org/sebastianbergmann/php-file-iterator)
+
+# php-file-iterator
+
+## Installation
+
+You can add this library as a local, per-project dependency to your project using [Composer](https://getcomposer.org/):
+
+    composer require phpunit/php-file-iterator
+
+If you only need this library during development, for instance to run your project's test suite, then you should add it as a development-time dependency:
+
+    composer require --dev phpunit/php-file-iterator
+