The link checker is failing without any errors

[brtkwr]

Describe the bug
Hello, thanks for this GH action. I tried to integrate it with my site but its failing for an unknown reason: https://github.com/brtknr/brtknr.github.io/runs/3473444040?check_suite_focus=true

To Reproduce
Steps to reproduce the behavior:

1. Run GH action
2. Look at the logs

Expected behavior
For the link checker to work or at least tell me why its failing.

[brtkwr]

Nevermind, I realised that removing FILENAME prints out the error on stdout. Would be helpful if this behaviour was documented! I'll create a PR.

[tushar5526]

It is failing due to https://github.com/victoriadrake/hydra-link-checker/blob/master/hydra.py#L283
Whenever there would be a broken link, the action would fail.