Fix FAQ Federation API link

Signed-off-by: Simó Albert i Beltran <sim6@probeta.net>

supporting-docs/guides/2015-08-19-faq.md

@@ -486,7 +486,7 @@ The Apache Licence is a permissive licence. We want the Matrix protocol itself t
 
 ##### Can I write a Matrix homeserver?
 
-Yes. Matrix is just a spec, so implementations of the spec are very welcome! It should be noted that as of October 2015, changes are still being made to the spec, so if you want to write a Matrix homeserver, it is strongly recommended that you chat to the Matrix.org devs in #matrix:matrix.org first! You can also read about the [Federation API here]( https://github.com/matrix-org/matrix-doc/blob/master/specification/30_server_server_api.rst).
+Yes. Matrix is just a spec, so implementations of the spec are very welcome! It should be noted that as of October 2015, changes are still being made to the spec, so if you want to write a Matrix homeserver, it is strongly recommended that you chat to the Matrix.org devs in #matrix:matrix.org first! You can also read about the [Federation API here](https://matrix.org/docs/spec/server_server/unstable.html).
 
 ##### How secure is this?