Merge pull request rust-lang#2300 from chiichen/dev/master/correct-config-to-bootstrap

doc: fix reference to #create-a-configtoml

Author: jieyouxu

src/doc/rustc-dev-guide/src/building/prerequisites.md

@@ -38,4 +38,4 @@ incremental compilation ([see here][config]). This will make compilation take
 longer (especially after a rebase), but will save a ton of space from the
 incremental caches.
 
-[config]: ./how-to-build-and-run.md#create-a-configtoml
+[config]: ./how-to-build-and-run.md#create-a-bootstraptoml