go.talk/present: fix a link.

R=golang-dev
CC=golang-dev
https://golang.org/cl/31770044
diff --git a/present/doc.go b/present/doc.go
index 254de64..846a531 100644
--- a/present/doc.go
+++ b/present/doc.go
@@ -24,6 +24,6 @@
 	.article      // article format, such as a blog post
 
 The present file format is documented by the present package:
-http://godoc.org/code.google.com/p/go.tools/godoc/present
+http://godoc.org/code.google.com/p/go.tools/present
 */
 package main