ukNum = function (parts) {
                var section = [];
                //fills the section part of the phone number with random numbers.
                parts.sections.forEach(function(n) {
                    section.push(self.string({ pool: '0123456789', length: n}));
                });
                return parts.area + section.join(' ');
            }
#Description:
===============================================
Generate a random Facebook id, aka fbid.

NOTE: At the moment (Sep 2017), Facebook ids are
"numeric strings" of length 16.
However, Facebook Graph API documentation states that
"it is extremely likely to change over time".
@see https://developers.facebook.com/docs/graph-api/overview/

#Examples:
===============================================
chance.fbid() => '1000035231661304'

@return [string] facebook id