context/ctxhttp: close httptest server

Change-Id: Ic8192f74337e021a5d72feb07b9648619d778235
Reviewed-on: https://go-review.googlesource.com/36673
Reviewed-by: Matt Layher <mdlayher@gmail.com>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
1 file changed