imports: fix TestFindImportVendor for 1.5 (fix build)
imports: fix TestFindImportVendor for 1.5 (fix build)

TBR=adonovan

Change-Id: I7edeb180bdf09648e7539b9371db0d14272b9030
Reviewed-on: https://go-review.googlesource.com/20697
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

golang/tools,golang/tools,syreclabs/go-tools,syreclabs/go-tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools,syreclabs/go-tools,golang/tools,golang/tools,syreclabs/go-tools