net/http: fix typo in comment

Change-Id: I753e62879a56582a9511e3f34fdeac929202efbf
Reviewed-on: https://go-review.googlesource.com/22680Reviewed-by: Ralph Corderoy <ralph@inputplus.co.uk>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/transport.go

@@ -2009,7 +2009,7 @@ type connLRU struct {
 	m  map[*persistConn]*list.Element
 }
 
-// addO adds pc to the head of the linked list.
+// add adds pc to the head of the linked list.
 func (cl *connLRU) add(pc *persistConn) {
 	if cl.ll == nil {
 		cl.ll = list.New()