Restore gobot's permission to cast TryBot-Result

gobot was using its membership of trybot-result-changers to do that,
but that group was switched to casting the vote on behalf of in
I90c09cba2e157152de6946f592f9833537841827

Change-Id: I94df0d7c546ecef94f783ff1f175374773ab43cc
Reviewed-on: https://go-review.googlesource.com/116764
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

project.config

diff --git a/project.config b/project.config
index 0ab6c4a..c0e2b09 100644
--- a/project.config
+++ b/project.config
@@ -55,6 +55,7 @@
 	editHashtags = group approvers
 	editHashtags = group gobot
 	labelAs-TryBot-Result = group trybot-result-changers
+	label-TryBot-Result = -1..+1 group gobot
 [access "refs/meta/config"]
 	exclusiveGroupPermissions = read
 	read = group Project Owners