[gmime] Updated REAMDE.md

[Jeffrey Stedfast <fejj src gnome org>]

commit 534e87e914a140d794e5f3fe0f8202005d05c9c2
Author: Jeffrey Stedfast <jestedfa microsoft com>
Date:   Wed Mar 8 15:36:40 2017 -0500

    Updated REAMDE.md

 README.md |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/README.md b/README.md
index b48ae43..4400328 100644
--- a/README.md
+++ b/README.md
@@ -256,7 +256,7 @@ g_mime_text_part_set_text (body, "Hey Alice,\n\n"
     "Will you be my +1?\n\n"
     "-- Joey\n");
 
-g_mime_message_set_mime_part (message, body);
+g_mime_message_set_mime_part (message, (GMimeObject *) body);
 g_object_unref (body);
 ```