Update rspec_junit_formatter requirement to ~> 0.4.0
Update rspec_junit_formatter requirement to ~> 0.4.0

Updates the requirements on [rspec_junit_formatter](https://github.com/sj26/rspec_junit_formatter) to permit the latest version.
- [Release notes](https://github.com/sj26/rspec_junit_formatter/releases)
- [Commits](https://github.com/sj26/rspec_junit_formatter/commits/v0.4.0)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
gocardless/prius