[C++] Update C++ Docs URL slug from cxx to cpp (#10)

* test breadcrumb to drivers home

* redirects

Author: rachel-mack

config/redirects

@@ -7,4 +7,4 @@ symlink: current -> master
 raw: ${prefix}/ -> ${base}/current/
 raw: ${prefix}/stable -> ${base}/current/
 raw: ${prefix}/master -> ${base}/upcoming/
-
+raw: /docs/languages/cxx -> /docs/languages/cpp