For package paths that include a "vendor" segment, use only the
portion of the path that comes after the final "vendor" segment, as
is done by the imports package.
Fixesgolang/go#17247
Change-Id: Ic83c4662cfddd1a696c206494b3a869e8c7dff5c
Reviewed-on: https://go-review.googlesource.com/29851
Reviewed-by: Alan Donovan <adonovan@google.com>
Rhys Hiltner