FEATURE: Changed awk config command to be more cross platform (#513)

FEATURE: Changed awk config command to be more cross platform (#513)

in Ubuntu 20.04 LTS, pre installed is mawk 1.3.4, which is called when you use awk. In this version, "--field-seperator" is not a valid option, leaving discourse-doctor with many errors.
Described in https://meta.discourse.org/t/discourse-doctor-parsing-smtp-credentials-not-working-admin-registration-email-not-working/174461, this commit aims to use -F as the accepted flag for field separation which is unambiguous across GNU AWK and Ubuntu MAWK.