Update CONTRIBUTING.md

diff --git a/doc/CONTRIBUTING.md b/doc/CONTRIBUTING.md
index 2369e5300152fa7424fc7c1c4cf61e13a286bdec..3b310985731c176e6d2e2946f5e351a91f7e1810 100644 (file)
--- a/doc/CONTRIBUTING.md
+++ b/doc/CONTRIBUTING.md
@@ -18,7 +18,7 @@ I follow the [Linux Coding Style][4] with the following variations:
 - Always use braces when using control structures.
 
 [1]: https://www.bell-labs.com/usr/dmr/www/cbook/
-[2]: http://www.x.org/releases/X11R7.5/doc/libxcb/tutorial/
+[2]: https://xcb.freedesktop.org/tutorial/
 [3]: http://git-scm.com/documentation
 [4]: https://www.kernel.org/doc/Documentation/process/coding-style.rst
 [5]: http://lea.verou.me/2012/01/why-tabs-are-clearly-superior/