Fix SIGINT checkClean should only log error instead throw error

Author: jackycute

app.js

@@ -639,7 +639,7 @@ process.on('SIGINT', function () {
     var checkCleanTimer = setInterval(function () {
         if (history.isReady() && realtime.isReady()) {
             models.Revision.checkAllNotesRevision(function (err, notes) {
-                if (err) throw new Error(err);
+                if (err) return logger.error(err);
                 if (!notes || notes.length <= 0) {
                     clearInterval(checkCleanTimer);
                     return process.exit(0);