http2: fix typo in ReadFrame

This fixes a minor typo in frame.go ReadFrame.

Change-Id: Idb6d4d412a6bc27fa8afb6f03007e974cd98d0c9
Reviewed-on: https://go-review.googlesource.com/24310
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>

http2/frame.go

@@ -454,7 +454,7 @@ func terminalReadFrameError(err error) bool {
 //
 // If the frame is larger than previously set with SetMaxReadFrameSize, the
 // returned error is ErrFrameTooLarge. Other errors may be of type
-// ConnectionError, StreamError, or anything else from from the underlying
+// ConnectionError, StreamError, or anything else from the underlying
 // reader.
 func (fr *Framer) ReadFrame() (Frame, error) {
 	fr.errDetail = nil