psr-7 attempt to set the Host header during construction

fixes: #172

Author: pine3ree

src/RequestTrait.php

@@ -69,6 +69,13 @@ private function initialize($uri = null, $method = null, $body = 'php://memory',
         list($this->headerNames, $headers) = $this->filterHeaders($headers);
         $this->assertHeaders($headers);
         $this->headers = $headers;
+
+        // per PSR-7: attempt to set the Host header from a provided URI if no
+        // Host header is provided
+        if (! $this->hasHeader('Host') && $this->uri->getHost()) {
+            $this->headerNames['host'] = 'Host';
+            $this->headers['host'] = [$this->getHostFromUri()];
+        }        
     }
 
     /**