updates: only send email notifications when not auto-updating

fixes #749

src/test/updatechecker-test.js

@@ -124,7 +124,7 @@ describe('updatechecker - box', function () {
             expect(updatechecker.getUpdateInfo().box.sourceTarballUrl).to.be('box.tar.gz');
             expect(scope.isDone()).to.be.ok();
 
-            checkMails(0, done); // it seems we stopped sending mails for box updates!
+            checkMails(1, done);
         });
     });