doc/install: specify clone -u instead of -r

R=rsc
CC=golang-dev
https://golang.org/cl/4435081
diff --git a/doc/install.html b/doc/install.html
index b989416..2256123 100644
--- a/doc/install.html
+++ b/doc/install.html
@@ -136,7 +136,7 @@
 Then check out the repository:</p>
 
 <pre>
-$ hg clone -r release https://go.googlecode.com/hg/ go
+$ hg clone -u release https://go.googlecode.com/hg/ go
 </pre>
 
 <h2 id="install">Install Go</h2>