Fix Backwards Incompatible Config Additions

[phily245]

What is the issue?

In https://github.com/ukfast/laravel-health-check/pull/53/files, new config values were added without a fallback.
This was a breaking change for those who have a custom config file, as the new config now returns null, so the paths change from /health and /ping to both be /.

Steps To Reproduce

• Update a laravel/lumen application with an existing custom config file to the latest version
• Hit /ping and /health
• Both get 404 responses

Expected behaviour

200 responses to /ping and /health instead of 404s

Possible fixes

Add a fallback to the config values

Additional context

N/a

[tylerwoonton]

Thanks for this. Let me know if you need anything else, @phily245!