shiny/vendor: make BurntSushi/xgb/xproto tests skip when $DISPLAY is empty

The builders don't have X. (notably Darwin)

Perhaps the Linux ones should. Or some should. Please file a separate bug for that.

Somebody else might want to upstream this fix to BurntSushi.

Updates golang/go#11811

Change-Id: I6d270a83fc59a3923723b5bfbd0b92057a484a1c
Reviewed-on: https://go-review.googlesource.com/12765
Reviewed-by: Nigel Tao <nigeltao@golang.org>
1 file changed