Since Go 1.10, they enabled vetting by default when running tests. This
reveals issues in the thests which should be fixed upstream, but for
now, disable vetting to let the tests pass again.
An upstream issue[0] has been created. Untill then, apply a patch to the
Makefile to disable vetting.
[0]: https://github.com/junegunn/fzf/issues/1236
