Added Sentry error capture for failed email update after sending is complete

refs https://github.com/TryGhost/Team/issues/1321

- when updating the Email record after submitting all email batches we have a `catch` call but it was only logging the error
- added a call to Sentry so there's more visibility if those saves fail

core/server/services/bulk-email/bulk-email-processor.js

@@ -130,6 +130,7 @@ module.exports = {
                 id: emailModel.id
             });
         } catch (err) {
+            sentry.captureException(err);
             logging.error(err);
         }