Failing checkAuthorEmails fuzz test

[kriswest]

Describe the bug
The fuzz test for checkAuthorEmails relies on random string generation NOT producing something that looks like a valid email address, however, it can happily do so and fail at random times:

The following commit author e-mails are legal: |*]@BGjZ
      1) should not crash on random string in commit email

The above example isn't particularly valid (no recognisable TLD) but is enough to fail the test.

Additional context

Could be fixed by making sure the strings never contain an @ character (by removing it if present)

[jescalada]

I solved this issue in #1158! Previously, we're simply checking for the "@" and splitting on it, so I replaced it with validator.isEmail that checks if it's compliant with the RFC definitions.