Add missing use statement (#189) (#190)

Author: YetiCGN

src/Psr17HttpProvider.php

@@ -4,6 +4,7 @@
 
 use Psr\Http\Client\ClientInterface;
 use Psr\Http\Message\RequestFactoryInterface;
+use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\StreamFactoryInterface;
 use Psr\Http\Message\ResponseInterface;