Why php-http/message-factory was reverted back to the composer.json

Hopefully merge issue has happened but the package deleted in #158 mystically reverted back:

https://github.com/florianv/exchanger/commit/09183c7a5a77b8d4a58f7cbf706903f7a136e571#diff-d2ab9925cad7eac58e0ff4cc0d251a937ecf49e4b6bf57f8b95aab76648a9d34R36

cc @florianv 