go/loader: fix ExampleConfig_Import (fix build)

TBR=adonovan

Tested against 1.6, 1.7, and 1.8.

Change-Id: Ifd8e02a83e7b92c00a746f10475ab725801199e2
Reviewed-on: https://go-review.googlesource.com/32638
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
1 file changed