Fix #41: Response builder broke header value

As specified at [RFC7230](https://tools.ietf.org/html/rfc7230#section-3.2.4), headers charset should be limited to US-ASCII.

Author: mekras

spec/Builder/ResponseBuilderSpec.php

@@ -32,4 +32,17 @@ function it_reads_headers_from_string(ResponseInterface $response)
         $this->beConstructedWith($response);
         $this->setHeadersFromString("HTTP/1.1 200 OK\r\nContent-type: text/html\r\n");
     }
+
+    /**
+     * @link https://github.com/php-http/message/issues/41
+     */
+    function it_not_broke_headers(ResponseInterface $response)
+    {
+        $response->withStatus(200, 'OK')->willReturn($response);
+        $response->withProtocolVersion('1.1')->willReturn($response);
+        $response->hasHeader('Content-type')->willReturn(false);
+        $response->withHeader('Content-type', 'application/xml+atom')->willReturn($response);
+        $this->beConstructedWith($response);
+        $this->setHeadersFromString("HTTP/1.1 200 OK\r\nContent-type: application/xml+atom\r\n");
+    }
 }

src/Builder/ResponseBuilder.php

@@ -135,8 +135,8 @@ public function addHeader($headerLine)
                 sprintf('"%s" is not a valid HTTP header line', $headerLine)
             );
         }
-        $name = trim(urldecode($parts[0]));
-        $value = trim(urldecode($parts[1]));
+        $name = trim($parts[0]);
+        $value = trim($parts[1]);
         if ($this->response->hasHeader($name)) {
             $this->response = $this->response->withAddedHeader($name, $value);
         } else {