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/go_spec.html b/doc/go_spec.html
index e62965a..3d11899 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -1,7 +1,7 @@
 <!--{
 	"Title": "The Go Programming Language Specification",
 	"Subtitle": "Version of Oct 3, 2013",
-	"Path": "/doc/spec"
+	"Path": "/ref/spec"
 }-->
 
 <!--