Fix link in contributing page

Author: floftar

CONTRIBUTING.md

@@ -307,7 +307,7 @@ are:
 [gsearchdocs]: https://www.google.com/search?q=site:doc.rust-lang.org+your+query+here
 [rif]: http://internals.rust-lang.org
 [rr]: https://doc.rust-lang.org/book/README.html
-[tlgba]: http://tomlee.co/2014/04/03/a-more-detailed-tour-of-the-rust-compiler/
+[tlgba]: http://tomlee.co/2014/04/a-more-detailed-tour-of-the-rust-compiler/
 [ro]: http://www.rustaceans.org/
 [rctd]: ./COMPILER_TESTS.md
 [cheatsheet]: http://buildbot.rust-lang.org/homu/