Can't make wait-on work in Github action

Hi Jeff.

Thanks for an awesome library, but I can't get it to work on Github actions.

I use this command:
```
npm run start:test & ./node_modules/.bin/wait-on http://localhost:3000 --timeout 120000 -v
```

I can tell from the output that the server is up and running on port 3000, but wait-on only prints this output:
```
2021-01-03 11:42:52 info: Express is 👂 on port 3000/graphql. (Pid 2995)
making HTTP(S) head request to url:http://localhost:3000 ...
HTTP(S) error for http://localhost:3000 Error: Request failed with status code 500
making HTTP(S) head request to url:http://localhost:3000 ...
HTTP(S) error for http://localhost:3000 Error: Request failed with status code 500
making HTTP(S) head request to url:http://localhost:3000 ...
HTTP(S) error for http://localhost:3000 Error: Request failed with status code 500
making HTTP(S) head request to url:http://localhost:3000 ...
HTTP(S) error for http://localhost:3000 Error: Request failed with status code 500
making HTTP(S) head request to url:http://localhost:3000 ...
HTTP(S) error for http://localhost:3000 Error: Request failed with status code 500
making HTTP(S) head request to url:http://localhost:3000 ...
HTTP(S) error for http://localhost:3000 Error: Request failed with status code 500
making HTTP(S) head request to url:http://localhost:3000 ...
HTTP(S) error for http://localhost:3000 Error: Request failed with status code 500
making HTTP(S) head request to url:http://localhost:3000 ...
HTTP(S) error for http://localhost:3000 Error: Request failed with status code 500
making HTTP(S) head request to url:http://localhost:3000 ...
```

When I test it locally it works perfect?