Rollup merge of rust-lang#24471 - andrewseidl:master, r=alexcrichton

Use external instead of relative link for rustbyexample.com in generated `src/doc/index.md`. (http://doc.rust-lang.org/nightly/index.html)

Previous: http://doc.rust-lang.org/nightly/rustbyexample.com
Desired: http://rustbyexample.com/

Author: steveklabnik

src/doc/index.md

@@ -19,7 +19,7 @@ ideas behind Rust.
 donated to the Rust project. As the name implies, it teaches you Rust through a
 series of small examples.
 
-[rbe]: rustbyexample.com
+[rbe]: http://rustbyexample.com/
 
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