Extract the default Slack options to a constant to ensure any uninitialized constant isn't hidden
requested to merge extract-slack-default-options-to-a-constant-to-ensure-uninitialized-constants-arent-hidden into master
Since we stub the #slack_messenger private method, we didn't catch the
unitialized GITLAB_BOT constant. Extracting the Slack options to a
constant hash ensures that it's evaluated when the class is loaded,
thus making the error visible.
Signed-off-by: Rémy Coutable remy@rymai.me