URL to Ruby's Rack [ci skip]

Author: olleolleolle

doc/us/index.html

@@ -54,7 +54,7 @@ <h2>Overview</h2>
 provide some kind of service to other applications, such as authentication,
 file uploads, request isolation, or multiplexing.</p>
 
-<p>WSAPI's main influence is Ruby's <a href="http://rack.rubyforge.org/">Rack</a> framework, but it was
+<p>WSAPI's main influence is Ruby's <a href="https://github.com/rack/rack">Rack</a> framework, but it was
 also influenced by Python's <a href="http://wsgi.org/wsgi">WSGI</a> (PEP 333). It's not a direct
 clone of either of them, though, and tries to follow standard Lua idioms.</p>