Update docs to new syntax.

Author: metajack

doc/rust.md

@@ -790,7 +790,7 @@ extern mod extra; // equivalent to: extern mod extra = "extra";
 
 extern mod rustextra = "extra"; // linking to 'extra' under another name
 
-extern mod foo = "some/where/foo#1.0"; // a full package ID for rustpkg
+extern mod foo = "some/where/rust-foo#foo:1.0"; // a full package ID for rustpkg
 ~~~~
 
 ##### Use declarations