[gitiles] do not allow .. in Treeish
[gitiles] do not allow .. in Treeish

R=2190fe9a39b4920ec7bd59c848ec5cccd163056f@chromium.org

Bug: 821287
Change-Id: I172547ad2f158eaec035e68be9706d522895ec69
Reviewed-on: https://chromium-review.googlesource.com/961394
Reviewed-by: Ryan Tseng <2190fe9a39b4920ec7bd59c848ec5cccd163056f@chromium.org>
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go