doc: move spec and memory model back to /ref/

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/14364043
diff --git a/doc/docs.html b/doc/docs.html
index 8c5d17a..7aad8da 100644
--- a/doc/docs.html
+++ b/doc/docs.html
@@ -85,12 +85,12 @@
 The documentation for the Go tools.
 </p>
 
-<h3 id="spec"><a href="/doc/spec">Language Specification</a></h3>
+<h3 id="spec"><a href="/ref/spec">Language Specification</a></h3>
 <p>
 The official Go Language specification.
 </p>
 
-<h3 id="go_mem"><a href="/doc/mem">The Go Memory Model</a></h3>
+<h3 id="go_mem"><a href="/ref/mem">The Go Memory Model</a></h3>
 <p>
 A document that specifies the conditions under which reads of a variable in
 one goroutine can be guaranteed to observe values produced by writes to the