The previous change updated the import of golang.org/x/tools/go/types
to the standard go/types package, causing 1.4 builds to fail.
Fixes#13874.
Change-Id: Idf0b4ac5e4e01dd5cd7cc9b89d017fbffb7a29df
Reviewed-on: https://go-review.googlesource.com/18430
Reviewed-by: Robert Griesemer <gri@golang.org>