http2: add missing import path declaration

Change-Id: Ic37b6b84bfc695cfb1ca7cf8e7da52c801e6d236
Reviewed-on: https://go-review.googlesource.com/25500
Reviewed-by: Chris Broadfoot <cbro@golang.org>

http2/http2.go

@@ -13,7 +13,8 @@
 // See https://http2.github.io/ for more information on HTTP/2.
 //
 // See https://http2.golang.org/ for a test server running this code.
-package http2
+//
+package http2 // import "golang.org/x/net/http2"
 
 import (
 	"bufio"