Minor fixes in comments

* Fix typo

"netowrk" is a misspelling of "network"

* Fix export comment

Comment on exported type Hub should be of the form "Hub ..." (golint)

examples/chat/hub.go

@@ -4,7 +4,7 @@
 
 package main
 
-// hub maintains the set of active clients and broadcasts messages to the
+// Hub maintains the set of active clients and broadcasts messages to the
 // clients.
 type Hub struct {
 	// Registered clients.

proxy.go

@@ -14,7 +14,7 @@ import (
 	"strings"
 )
 
-type netDialerFunc func(netowrk, addr string) (net.Conn, error)
+type netDialerFunc func(network, addr string) (net.Conn, error)
 
 func (fn netDialerFunc) Dial(network, addr string) (net.Conn, error) {
 	return fn(network, addr)