Refine regex for detecting fake fax communications

[peterdj45]

Updated regex patterns to improve detection of fake fax messages.

Description

updated regex keyword to account for samples beginning with fr (possible shorthand for fax received)

Associated samples

• https://platform.sublime.security/messages/4f9fd176de65a389de4e0b22a389e94e822a9ffd3cd49faace0dcb6fdfbd8a8c

Associated hunts

• https://platform.sublime.security/messages/hunt?huntId=019a5691-795a-7e0e-85dd-4cfa068320da