go.net/proxy: fix typo in doc

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/12702044
diff --git a/proxy/proxy.go b/proxy/proxy.go
index b6cfd45..8ccb0c5 100644
--- a/proxy/proxy.go
+++ b/proxy/proxy.go
@@ -24,7 +24,7 @@
 	User, Password string
 }
 
-// DefaultDialer returns the dialer specified by the proxy related variables in
+// FromEnvironment returns the dialer specified by the proxy related variables in
 // the environment.
 func FromEnvironment() Dialer {
 	allProxy := os.Getenv("all_proxy")