http2: fix typo in comment

Change-Id: I0febb967cf55118693952332bbb6f740616cfd39
Reviewed-on: https://go-review.googlesource.com/44271
Run-TryBot: David Lazar <lazard@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

http2/configure_transport.go

@@ -56,7 +56,7 @@ func configureTransport(t1 *http.Transport) (*Transport, error) {
 }
 
 // registerHTTPSProtocol calls Transport.RegisterProtocol but
-// convering panics into errors.
+// converting panics into errors.
 func registerHTTPSProtocol(t *http.Transport, rt http.RoundTripper) (err error) {
 	defer func() {
 		if e := recover(); e != nil {