Ignore SECURITY file when scanning timezones #134

Problem:

The Arch Linux core package tzdata adds a SECURITY file in /usr/share/tzinfo since tzdata version 2021c-1.

This file is basically a note to report security-related bugs to the right person:

Please report any sensitive security-related bugs via email to the
tzdb designated coordinators, currently Paul Eggert
<eggert@cs.ucla.edu> and Tim Parenti <tim@timtimeonline.com>.
Put "tzdb security" at the start of your email's subject line.
We prefer communications to be in English.

[...]

tzinfo wants to use this file, which leads to an error.

How to reproduce:

Using Ruby IRB:

>> require 'tzinfo'
=> true
>> TZInfo::Timezone.all.find_all {|tz| tz.current_period.abbreviation == :some_abbrev }
TZInfo::InvalidTimezoneIdentifier (The file '/usr/share/zoneinfo/SECURITY' does not start with the expected header. (loading SECURITY))

Information:

Fix:

I propose this PR to exclude the SECURITY file from beeing used by tzinfo.