Bump eventsource from 1.0.7 to 1.1.1 in /sample-app/front-end

Bumps [eventsource](https://github.com/EventSource/eventsource) from 1.0.7 to 1.1.1.
- [Release notes](https://github.com/EventSource/eventsource/releases)
- [Changelog](https://github.com/EventSource/eventsource/blob/master/HISTORY.md)
- [Commits](EventSource/eventsource@v1.0.7...v1.1.1)

---
updated-dependencies:
- dependency-name: eventsource
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]