servo: Merge #5579 - Use canonical GitHub URL for Rust (from dhodder:master); r=Ms2ger

Although https://github.com/mozilla/rust successfully redirects, it's no longer the official GitHub URL for Rust.

Source-Repo: https://github.com/servo/servo
Source-Revision: 74afd086d2ce5a5631a63a1f6642cfc0de5dfef7

servo/README.md

@@ -1,7 +1,7 @@
 # The Servo Parallel Browser Project
 
 Servo is a prototype web browser engine written in the
-[Rust](https://github.com/mozilla/rust) language. It is currently developed on
+[Rust](https://github.com/rust-lang/rust) language. It is currently developed on
 64bit OS X, 64bit Linux, Android, and Gonk (Firefox OS).
 
 Servo welcomes contribution from everyone.  See