Fix balance update criteria

Include issue.is_open status when considering a bounty open.

Fixes: #151

resources/sql/queries.sql

@@ -493,7 +493,8 @@ SELECT
 FROM issues i, repositories r
 WHERE r.repo_id = i.repo_id
 AND contract_address IS NOT NULL
-AND i.confirm_hash IS NULL;
+AND i.confirm_hash IS NULL
+AND i.is_open = true;
 
 -- :name get-bounty :? :1
 -- :doc details for a bounty issue given owner, repo and issue nunber