doc: update go1.3.txt for regexp change

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/72640043

doc/go1.3.txt

@@ -18,6 +18,7 @@ net/http: use TCP keep-alives for ListenAndServe and ListenAndServeTLS (CL 48300
 net: add Dialer.KeepAlive option (CL 68380043)
 net: enable fast socket creation using SOCK_CLOEXEC and Accept4 on FreeBSD 10 (69100043)
 os/exec: fix Command with relative paths (CL 59580044)
+regexp: add one-pass optimization from RE2 (CL 13345046)
 runtime/debug: add SetPanicOnFault (CL 66590044)
 runtime: output how long goroutines are blocked (CL 50420043)
 sync: add Pool (CL 41860043, 46010043)