[gitg] Fix diff function context trimming

[Jesse van den Kieboom <jessevdk src gnome org>]

commit d0394b3d6d1b6230f8ed3028d5853a089414130b
Author: Jesse van den Kieboom <jessevdk gmail com>
Date:   Tue Dec 23 17:42:23 2014 +0100

    Fix diff function context trimming

 libgitg/gitg-diff-view-request-diff.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgitg/gitg-diff-view-request-diff.vala b/libgitg/gitg-diff-view-request-diff.vala
index 694ecdb..0363137 100644
--- a/libgitg/gitg-diff-view-request-diff.vala
+++ b/libgitg/gitg-diff-view-request-diff.vala
@@ -161,7 +161,7 @@ namespace Gitg
 
                        if (pos >= 0)
                        {
-                               h = h[pos + 2:-1].chug();
+                               h = h.substring(pos + 2).chug();
                        }
 
                        builder.set_member_name("header").add_string_value(h);